The Silversmith's Handbook / Containing full instructions for the alloying and working of silver

THE

SILVERSMITH’S HANDBOOK

BY THE SAME AUTHOR, UNIFORM WITH THE PRESENT VOLUME.

Ninth Impression, price 5s. net, cloth.

THE GOLDSMITH’S HANDBOOK,

CONTAINING

FULL INSTRUCTIONS FOR THE ALLOYING AND WORKING OF GOLD.

Including the Art of Alloying, Melting, Reducing, Colouring, Collecting, and Refining; The Processes of Manipulation, Recovery of Waste; Chemical and Physical Properties of Gold; with a New System of Mixing its Alloys, Solders, Enamels, and other Useful Rules and Recipes.

Crown 8vo, price 3s. 6d. net, cloth.

THE

HALL-MARKING OF JEWELLERY,

PRACTICALLY CONSIDERED.

Comprising an account of all the different Assay Towns of the United Kingdom, with the Stamps at present employed; also the Laws relating to the Standards and Hall Marks at the various Assay Offices; and a variety of Practical Suggestions concerning the Mixing of Standard Alloys, and other Useful Information.

CROSBY LOCKWOOD & SON,

7, Stationers' Hall Court, Ludgate Hill, E.C.

THE

SILVERSMITH’S HANDBOOK

CONTAINING

FULL INSTRUCTIONS

FOR THE

ALLOYING AND WORKING OF SILVER

INCLUDING THE DIFFERENT MODES OF REFINING AND MELTING
THE METAL; ITS SOLDERS; THE PREPARATION OF IMITATION
ALLOYS; METHODS OF MANIPULATION; PREVENTION OF
WASTE; INSTRUCTIONS FOR IMPROVING AND
FINISHING THE SURFACE OF THE WORK
TOGETHER WITH OTHER USEFUL
INFORMATION AND MEMORANDA

By GEORGE E. GEE

GOLDSMITH AND SILVERSMITH

AUTHOR OF “THE GOLDSMITH’S HANDBOOK,”
“THE HALL-MARKING OF JEWELLERY,” ETC. ETC.

LONDON

CROSBY LOCKWOOD AND SON

7, STATIONERS' HALL COURT, LUDGATE HILL
1921

PRINTED BY
WILLIAM CLOWES AND SONS, LIMITED,
LONDON AND BECCLES.

[PREFACE.]

The object of this Treatise is to supply a want long felt in the Silver Trade, namely, a work of reference from which workmen, apprentices, and manufacturers, employing the material upon which it treats, may find information which will be of assistance to them in the performance of their daily duties, and by which their operations may be rendered more successful. The Author was led to undertake the present work from having had many opportunities, during his lengthened experience in the art of silver-working, of observing the difficulties and stumbling-blocks that are constantly to be met with in the manifold branches of this important trade, by those practically engaged in it, and also by those persons who are desirous of acquiring a thorough knowledge of the mechanical and manipulative details belonging to it. To assist his object, numerous illustrations have been prepared for this Treatise, with the view of rendering the various processes of the art more readily comprehensible, and to save a lengthened or detailed description of them.

The different modes of alloying and melting silver; its solders; the preparation of imitation alloys; methods of working; the prevention of waste; instructions for improving and finishing the surface of the work, together with other useful information and memoranda—all these have been carefully collected and placed in order in the body of the work.

The Author has endeavoured, throughout, to present the contents (which he has with some little difficulty and labour brought together) in as practical and readable a form as is compatible with accuracy and efficiency.

G. E. GEE.

[PREFACE TO THE SECOND EDITION.]

Since the publication of the first edition of this work important changes have taken place in the commercial value of silver, its present cost in the best markets being sixpence per ounce lower than it was when this volume first appeared in 1877. This depreciation in value has, of course, necessitated a thorough revision of the former prices of the various alloys, solders, and other substances mentioned throughout the work; and this has been done in order to render it the more complete as a work of general reference, conveying correct and useful information to the reader. The Author trusts that his endeavours in this direction will be appreciated.

58, Tenby St. North, Birmingham.
February, 1885.

[PREFACE TO THE FOURTH EDITION.]

In issuing the present edition, a few introductory remarks are necessary to explain that numerous revisions have been made in Chapters VI. and VII. (by means of the Tables referred to below) regarding the cost prices of the different alloys, solders, etc., which I trust will increase the value of the book.

Through the repeal of the silver duty in the year 1890, a great impetus has been given to the Silver industry of this country, and notwithstanding the length of time that has elapsed since this book was first published, a steady demand has continued for its possession by workers in the precious metal trades—a fact which is gratifying to the Author, not only because a reprint is again called for, but as showing that the work has held its position, and may now justly claim to be a standard authority on the subject of which it treats.

It has not been found necessary to interfere with the general processes embodied in the book, as they are practically the same as formerly; but as regards the commercial value of silver, there is again a considerable depreciation[A] to record on the prices prepared for the second edition in 1885, and it becomes imperative that this depreciation should be dealt with in this new edition, in order to bring the work up to date.

[A]

The market price of silver has for many years been of a very variable nature, almost each day’s prices showing a difference, so that it would be impossible to provide the reader with an unvarying fixed price per ounce. The best and most practical thing to do under the circumstances, it seemed, was to carefully revise the different cost prices of the alloys and solders specified in Chapters VI. and VII. and give them by way of approximate Tables, compiled for each chapter separately. These two Tables follow this Preface (making pp. ix. and x.) and will serve as a ready reference for present workers in the silver trades. Thus, by bringing the figures down to date, the work may still retain its reliable character as a practical guide to the silversmith’s workshop.

G. E. GEE.

58, Tenby St. North, Birmingham.
January, 1907.

[PUBLISHERS' NOTE TO FIFTH EDITION.]

In February 1921 silver was quoted at 34½d. to 36-1/8d., and it is therefore sufficient to note that the prices at that date correspond approximately to those current in 1907. It should be noted that the melting of British gold and silver is prohibited, as well as their export.

Table of Revised and Up-to-date Cost Prices of the Different Alloys in [Chapter VI].

This Table is based on the market price of fine silver being 3/- per ounce.

Table of Revised and Up-to-date Cost Prices of the Different Solders in [Chapter VII].

This Table is based on the market price of fine silver being 3/- per ounce.

[CONTENTS.]

INTRODUCTORY CHAPTER.

CHAPTER I.

Silver.

CHAPTER II.

Sources of Silver.

CHAPTER III.

The Assay of Silver Ores.

CHAPTER IV.

The Cupellation of Silver Ores.

CHAPTER V.

The Alloys of Silver.

CHAPTER VI.

Various Qualities of Silver.

CHAPTER VII.

Silver Solders: their Uses and Applications.

CHAPTER VIII.

On the Melting of Silver.

CHAPTER IX.

On the Working of Silver.

CHAPTER X.

Enriching the Surfaces of Silver.

CHAPTER XI.

Imitation Silver Alloys.

CHAPTER XII.

Economical Process.

CHAPTER XIII.

Licences and Duties.

CHAPTER XIV.

Useful Information for the Trade.

CHAPTER XV.

THE

SILVERSMITH’S HANDBOOK.

[INTRODUCTORY CHAPTER.]

In reviewing the rise and progress of the silversmith’s beautiful and interesting art, in its relation to the manufacture of articles of personal ornament and luxury at home and abroad, we may observe at the outset, that the material of which they are composed differs widely in character from that employed by the ordinary “metalsmiths” and the manufacturer of “electro-plated wares.” Silver, the material of which we are now treating, being a precious metal and of considerable value, it is essentially necessary that the most careful means be exercised in dealing with it from the commencement—that is, from the pure or fine state—and also that the utmost economy be observed in reference to the kind of mechanical treatment to which it is subjected in the production of the silversmith’s work, in order to prevent too great a quantity of waste or loss of material. For it should be borne in mind that silver, like gold, begins to lose, in one way or another, every time it is touched; therefore, carefulness and economy will be the characteristics of our teaching, so far as regards the present subject.

The vast majority of working silversmiths know very little of the physical and chemical properties of the metal they employ, and still less of the comparison it bears with other metals in the field of science; and this want of scientific knowledge is nowhere more apparent than in our own country, where the English workman, in art education, is much behind the foreigner; and yet we have some of the finest and best workmen, in their special branches, in the whole world. The English workman believes that if the work is worth doing at all, it is worth doing well; and we have no hesitation in saying, that, if a good technical education were afforded, concerning the precious metal trades, he would scarcely have an equal, and certainly no superior, abroad, in art workmanship, both in respect to the display of good taste and judgment, combined with a knowledge of design, so far as the exercise of these qualities is compatible with the manufacture of articles specially designed for use and ornament.

The object of the information we are about to supply is to enable the practical silversmith to become a perfect master of his art or profession; and such a condition, when once achieved, will be found of considerable assistance to him in the various kinds of manufacture that present themselves; so that he will know how to begin a piece of work and when to leave it off; be able to remedy a defect in the metal when required, as well as be in a position to form an opinion as to the relative treatment of its different alloys; all of which invariably require different treatment.

We shall commence by describing the characteristics of fine silver, carefully narrating the distinctive features of its alloys; then give an account of the processes employed, mechanical and chemical, in the silversmith’s workshop; and conclude by pointing out the difference between English and foreign work in regard both to style and workmanship.

It may be thought by the reader, if uninitiated in the art, that the costly plate and other articles made from the precious metal are manufactured from entirely pure silver, and therefore that they possess absolute freedom from alloy; but this is not the case. Pure silver being far too soft to stand the necessary wear and tear of (metallic) life, it is mixed with some other metal, to give it increased hardness. In the manufacture of plate and ornamental wares the metal employed is always copper, in various proportions, thus forming different commercial qualities; and of these we shall speak hereafter. Our first object is to treat of the chemical and physical properties of the pure metal.

[CHAPTER I.]

Silver.

Pure silver is, next to gold, the finest metal, but of a smoother and more polished nature. It may be said to be almost infinitely malleable, but it will not so easily yield or extend under the hammer as fine gold. As a malleable metal, however, it stands next to it in this respect. It is characterized by its perfectly white colour, being the whitest of all the metals. It is harder than gold, yet in a pure state it is so soft that it can easily be cut with a knife. On account of its extreme softness, when in a pure state, it is employed for filigree work, being utterly devoid of that elastic power which is found in the metal when alloyed. It is for this reason that the Indian filigree workers, who are the finest in the world, are so very particular about the absolute purity of the metal before commencing the manufacture of their artistic work; all of which is exceedingly beautiful.

It is reported that fine silver is capable of being beaten into leaves of less than one-hundred-thousandth part of an inch in thickness. For the accuracy of this statement we cannot vouch, never having had occasion to try the experiment; its employment in that form being unknown in the ordinary industrial pursuits. Fine silver is extremely ductile, and may be drawn into the very finest wire without breaking, and almost without annealing. Its purity can be partly ascertained by the latter process; for perfectly fine silver never changes colour by heat, whereas when it contains alloy it blackens if heated in contact with a current of air, and soon hardens in wire-drawing.

Silver was a metallic element known to the ancients, and it is repeatedly mentioned in the Holy Scriptures. In the time of the patriarchs we read of it as having been constantly employed in the transactions of nations, and that it was in use as a standard of value; thus forming a circulating medium for the purpose of exchange. This function it has always continued to fulfil down to the present day, except that since the year 1816 it has not been so employed in the English currency. However, as token money, it is everywhere recognised as a circulating medium of trade. The Egyptian symbol for silver was represented by [Fig. 1], relating to the moon; in modern chemistry it is understood by ag. from the Latin name argentum, denoting silver.

Luna. Fig. 1.
Egyptian mark for Silver.

Fine silver is capable of receiving a polish scarcely inferior in lustre to that of highly polished steel, and in this state it reflects more light and heat than any other metal, without any perceptible change of colour for some considerable time. It is chiefly on this account, as well as its resistance to oxidation in air and water, that it is used for such a variety of purposes, not only of ornament and luxury, but also in a domestic way. Silver, unlike gold, cannot resist the influence of sulphuretted hydrogen, from the action of which it very soon becomes much tarnished if left exposed in damp rooms, &c.

Silver ranks next to gold in point of ductility and malleability. When pure, its density, or specific gravity, lies between 10.47 and 10.50, taking water as 1, according to the degree of compression it has received by rolling and hammering. It is fusible at a full red heat, or about 1873° Fahr. It is a metal having a very low radiating power for heat; hence silver wire of given dimensions retains and conducts heat better than a similar piece of another metal; for the same reason, a liquid contained in a silver vessel retains its heat much longer than if placed in one made of some other substance. Silver volatilises when subjected to a very great temperature in the fire, emitting rather greenish fumes. It loses between 2/21sts and 3/25ths, in proportion to its impurity, of its absolute weight in air when weighed in water. In point of tenacity it occupies the fifth position among the useful metals. In hardness it lies between copper and gold; and a small addition of the former substance considerably increases this quality, in which state it is largely employed in the arts. Nitric acid is the proper solvent for silver, as it dissolves it with the greatest ease and rapidity, forming nitrate of silver, which is much used for medical purposes, and in art. Sulphuric and hydrochloric acids act upon it but slowly in the cold. Silver resists partially the best aqua-regia, probably on account of the dense chloride which forms on the surface of the metal, from the action of the hydrochloric acid in the mixture of aqua-regia.

Fine silver is largely used in the industrial and commercial arts, in the manufacture of silver lace and fine filigree work; the latter branch being more commonly practised in India, Sweden, Norway, and some parts of Germany, where labour is cheap, than in England. This class of silversmith’s work takes a long time to produce, and as labour forms the chief item of its cost, this, not unnaturally, acts as a great drawback in the extension of the art of very fine filigree working, in all its intricate variety, in countries where labour is dear. To this subject we shall subsequently refer again in detail. Fine silver, with a small proportion of alloy, is largely used by all nations for purposes of coinage. It amalgamates with nearly all the metals, but is principally used in alloys suitable to the watchmaker’s and silversmith’s art. The purchasable price of fine silver for manufacturing purposes, which in 1884 was 4s. 8d. is now, 1921, 3s. per ounce, troy weight, varying however in value according to the total amounts purchased; for which see refiners' and assayers' charge lists, to be procured at the offices of any bullion dealer. The silver ores of commerce have generally an intermixture of a small quantity of gold, and sometimes instances have occurred in which it has been employed in manufactures without a proper chemical investigation; and in such cases the loss resulting from the omission would have amply paid the expenses of the process.

Exposed to the action of hot and concentrated sulphuric acid, silver dissolves, setting free sulphurous acid. By the application of this process—which is one of the most advantageous methods—silver may readily be separated from gold, sulphuric acid having no action upon the latter metal. With the exception of gold, silver perhaps more perfectly resists the action of the caustic alkalies and the powerful effects of nitre (saltpetre) than any other metal, if we omit platinum from the list of elements at present known to metallurgical chemistry. For reasons such as these its superiority for the manufacture of utensils for culinary and other domestic purposes is at once apparent, and because it is a metal upon which vegetable acids produce no effect.

[CHAPTER II.]

Sources of Silver.

Strictly speaking, silver mining does not exist as a distinct operation in Great Britain, for it can hardly be said that this country possesses any great quantity of silver ore. Yet we must not disguise or leave unnoticed, in dealing with this subject, the positive fact that silver is found to some extent in our copper and lead mines, principally in the latter; but in no case, as far as we know, have mines been worked for the sake of the silver alone. It is almost always found in conjunction with lead, and it is from that source that we have a good supply of British silver. The average annual yield in the British Isles for some years has been equal to 800,000 ounces—a position in regard to the quantity produced ranking second only to Spain amongst the nations of the world, America, of course, being excepted. Silver is found in a native state, the commonest ore being a sulphuret.

The chief European supplies are derived from Spain, in which country genuine silver ore exists; from Saxony and Prussia, where the ores are principally associated with lead, as in England; and from Austria, where it is for the greater part found mixed with copper. Silver is nearly always to be found in copper and lead mines, but generally in such small quantities that it is rarely worth the trouble and expense of separation.

Considerably more than three-fourths of the whole total supply of silver comes from America; and in fact nearly the whole territory of America is said to be more or less argentiferous. Until lately Mexico carried off the palm, as containing and yielding the largest percentage of silver; but through the discovery of another mine in the United States, at Nevada, of considerable richness, which has yielded enormous supplies, we shall not be far wrong in pronouncing the silver mines in the State of Nevada to be the richest in the whole world. The extensive production of these mines, combined with other causes, has led to a considerable depreciation in the value of silver, and probably this may yet lead to its more extensive employment in the arts and manufactures; and, in the midst of the very general depression of the jewellery trade, any change extending in that direction would be joyfully accepted by the thousands of workmen in the precious metal trades now standing idle. We are told that, since the year 1860, the production of silver has increased from an average yield of eight or nine to fourteen millions per annum, or about 60 per cent.; while, on the other hand, the foreign demand for the metal (formerly largely employed for the currency) has greatly diminished. The rise in cost of silver during the war years and those immediately following necessitated an Act in Great Britain “to amend the law in respect of the standard fineness of silver coins current in the United Kingdom and in other parts of His Majesty’s Dominions.”

The chief sources of supply in the British Isles, according to Professor George Gladstone, are as given below; and as all the silver found in this country is produced from lead ores, the average yield here given must be understood to exist in about that proportion to every ton of lead ore assayed:—Isle of Man, 50 to 60 oz.; Cornwall, about 30 oz.; Devonshire, about 30 oz.; Cardiganshire, 15 to 20 oz.; Montgomeryshire, 15 to 20 oz. Thus, it will be seen the lead ores of the Isle of Man yield the greatest proportion of silver in the British dominions. Silver is also found in the undermentioned counties, in all of which it is produced from lead ore:—Cumberland, Durham, and Northumberland, Denbighshire, Flintshire, and Derbyshire; but the percentage is much smaller than in the preceding cases. Ireland also yields a fair percentage of silver.

[CHAPTER III.]

The Assay of Silver Ores.

A large proportion of the silver of commerce is extracted from ores (which are too poor to allow of their being smelted or fused) by a process called amalgamation. Founded on the ready solubility of silver, &c., in metallic mercury, the ore is first crushed to powder, then mixed with common salt, and afterwards roasted. By the adoption of this plan the silver is reduced to a state of chloride. The roasting is done in a reverberatory furnace, in which the heat is very gradually raised, the ore being constantly stirred; the heat is then increased sufficiently to raise the ore to a good red heat. It is then put into wooden barrels, revolving on iron axles attached to the ends, and scraps of iron are then added to it; both are then agitated together by rotary motion, the effect of which is to reduce the chloride of silver to a metallic state. When this is effected, it is again agitated with mercury, and a fluid amalgam is formed with the metal, together with any other metallic ingredient that may happen to be present in the roasted ore. Subsequently, to recover the silver, the mercury is driven off by heat, and the silver is thus left behind in an impure state.

There are three ways of assaying silver ores; they are in the test assay as follows:—

1. Melting in a crucible.
2. Scorification.
3. Cupellation.

In the crucible assay the ore is commonly run down with a suitable flux, those most frequently employed being litharge, carbonate of soda, borax, and charcoal. These four substances are all that are required by the practical assayer in the treatment of the regular ores of silver.

Fig. 2. Fire-clay Crucible.

The assaying of the genuine ores is performed in the following manner; that is, if they contain but little earthy matter. They may then be conveniently treated by fusing with carbonate of soda, on account of its cheapness, and borax, in a fire-clay crucible ([Fig. 2]). The dimensions of the crucible should be as follows: 4½ inches in height, and 2½ inches in its greatest diameter, which should be at the top. A quantity of litharge (a semi-vitrious substance, oxide of lead), more than is actually necessary to take up the whole of the silver in the ore, should be added, so as to promote fusion, and collect the ingredients into one mass at the bottom of the crucible. In preparing the ore for the crucible, it must be well pounded, and intimately mixed with the undermentioned chemicals:—

Place two crucibles to warm during the time occupied in the preparation of the mixture, then put it into the warm crucible; take 100 grains more of litharge, and powder it over the contents in the vessel. Prepare in this manner a second mixture for the other crucible, place them both in the furnace, and put plenty of coke round them. The mixtures may be melted in an ordinary wind or melting furnace, such as is used by jewellers in the preparation of their material for art working. The fusion should take place very gradually at first, as silver in combination with lead is sensibly volatile at a high temperature: it may then be continued at a low heat for twenty-five minutes, and finally the operation may be completed with a full red heat for five minutes longer.

During the process of fusing the contents of the crucible may be watched by removing one of the bricks from the top of the furnace, and when the whole mass has become quite liquid the crucible must be seized with a pair of suitable tongs, tapped once or twice very lightly against the side of the furnace to procure the settlement of the contents, and immediately poured into an iron mould, previously warmed and greased to prevent adhesion and spitting. Allow the mould to remain for some time, in order to partially cool, and then plunge it into a vessel of cold water. On cooling, the metallic elements will be found incorporated into a button, the slag can then easily be removed by tapping with a hammer on the edge, and the plunging into cold water greatly facilitates this separation. The whole mass has then to be cupelled, in order to separate the silver from the lead and other metals.

Fig. 3. Fire-clay Fusing Cup.

Silver ores, containing a large proportion of the sulphides (chemical combinations of sulphur with metallic substances) of other metals, may be easily assayed by the scorification process, which is, without exception, applicable to the assay of all kinds of argentiferous ores; and is one of the best, most simple, and most exact methods that can possibly be employed in the extraction of silver from its ores. This process, like that of fusion with litharge, already described, has the effect of producing an alloy, and subsequently requires cupellation. The ore is first well pounded, and then put into a small shallow vessel made of close-grained refractory fire-clay ([Fig. 3]), with an excess of finely granulated lead and some borax. The fusing cup or scorifier employed in this process should be about 1½ in. high and 2½ ins. in its greatest diameter; some assayers, however, use them deeper in proportion to their width, and representing in form the end of an egg. The object of this shape is to preserve the bath of molten metal at the bottom, and that it may always be well covered and protected by the slag on the top during the process of fusing. In the scorification method the principles are exactly the reverse of those of the crucible assay; for in the latter the object is to reduce the oxide of lead to a metallic state, whereas in the former the metallic lead added to the pounded ore in the scorifier is oxidized by being fused in contact with the air. The charge for this assay may be as follows:—

The cups or scorifiers should be charged in the following manner: well mix the silver ore with 300 grains of granulated lead; place this mixture in a scorifier, and add 300 grs. more of granulated lead, and over the top of the whole put the burnt borax. The vessel may then be placed in an ordinary assay furnace or muffle, as many being introduced at one time as there is room for in the furnace, and submitted to the strongest heat for about thirty minutes; during the greater portion of this time the door should be kept closed, especially for the first fifteen minutes. On opening the muffle-door a current of air passes through the furnace, converting a portion of the lead into litharge; this enters into combination with the earthy portions of the ore, the other metallic sulphides, and also the borax, producing a fusible slag on the surface of the metallic bath, extending over the whole surface of the scorifier. The excess of lead is thus protected by this film or flux from the oxidizing effects of the currents of air admitted into the furnace, and remains united with whatever silver there may be in the ore, in a metallic state.

The fusing should be continued longer than the thirty minutes—in fact until the slag or flux is reduced into a perfectly liquid state; stirring it well with a slender iron rod will facilitate the operation, as it will tend to mix with the mass any hard portions remaining undissolved and attached to the sides or other parts of the vessels. This condition of the flux is absolutely indispensable; when the slags are quite liquid, which with a strong fire will take place in from thirty to forty minutes, wrap up in a piece of paper the powdered anthracite, and drop it into the scorifier while still in the furnace or muffle. The object of adding the anthracite at the last moment is to reduce any minute portions of the metal that may exist in the slags, and remain separated from the bulk. When the anthracite has burnt off, which process usually takes about five minutes, this point is considered to have been attained, and the operation is then complete. The scorifier may be immediately withdrawn from the fire, and the contents poured into a suitable casting-mould, of the form represented in [Fig. 4], a button of silver lead being the result. When cold, the metallic mass is readily separated from the slag or flux by slightly tapping with a hammer; the former may then be passed on to the next operation, viz. to be purified of its lead by the process of cupellation, which will be presently described.

When there is not enough borax present the assayer will observe an infusible skin floating upon the surface; should this be the case more borax must at once be employed, in order to dissolve such impurity. When a chloride of silver ore is to be assayed, carbonate of soda must be added to the mixture to prevent sublimation.

The following method of assaying is adopted in several large Continental establishments, where the ores have, beside the usual earthy matter and the sulphides of lead, an admixture of zinc, iron, and copper. The process is precisely similar to the crucible assay, in the case of genuine silver ores, as already described—with this exception, that no more lead is added than the ores then contain—that is, if we are treating galena or silver lead; other ores require different treatment according to their known composition. In this process wrought-iron crucibles are employed having the form and shape as shown in [Fig. 5]. They are made of thick iron plate, and are rendered secure by welding the edges firmly together. Their dimensions are as follows: a depth of 4½ ins., with a thickness of iron at the bottom of 1½ in., and a ¼ of an inch in the sides; the diameter at the top of the crucible should be about 2½ ins., and at the bottom between 2 and 2¼ ins. A mechanical mixture or flux is prepared to use with the ores to which we have referred, consisting of the following chemicals, all of which should be finely powdered and well mixed with the ore to be assayed:—

The furnace used for this assay is the ordinary one, having rather a high chimney, to insure a perfect draught. In effecting the reduction of the silver, the crucible is first placed as before on the fire, and allowed to become hot; when this is accomplished, take

These ingredients should be thoroughly mixed together, and put into the red hot crucible. Fuse at a low heat for about twenty minutes, when the whole will be in a perfect state of fusion; then give about five minutes strong heat, and at the end of that time the crucible may be withdrawn, and its contents poured into an iron mould, as represented in [Fig. 4], having one or two conical holes for the reception of the fused mass. The silver and lead collect at the bottom of the mould by reason of its high specific gravity. It may be removed by reversing the position of the latter, when a gentle tap or two will deprive it of that slag or flux which is usually attached to it. A large quantity of silver can be readily collected from its ores by an alternate use of crucibles, in which case it is possible to make a regular number of fusions per hour. Wrought-iron crucibles, when strongly prepared and carefully made, will stand about thirty of these fusions, giving way in the end on account of the action of the sulphur contained in the ores.

Fig. 4. Iron Casting-moulds.

Another kind of crucible, in addition to those already mentioned, is used by the trade, and is recommended by many assayers as superior to all others. [Fig. 6] represents the form of it. It is about 4½ ins. high, and 2 ins. in its greatest interior diameter, being in the form of a skittle. The charge consists of the following in this assay:

Put the powdered ore into the crucible, and place upon it the iron, which should not be in the form of filings or dust, but in small pieces; upon the ore and iron should be put the black flux, and lastly the common salt must be placed above all these substances as a protection against the air. The crucibles, as many as convenient, may now be introduced into the furnace, and slowly raised to a strong red heat, at which temperature they should be kept for about half an hour; at the end of that period they should be removed from the fire, slightly tapped to settle the contents, and then placed aside to cool. When this has taken place, a few blows with a hammer near the base of the crucibles, each in turn, will soon expose the button of silver attached to the undecomposed iron; the latter substance may, however, be easily detached by a few well-directed blows with the hammer.

In order to ascertain the exact amount of the precious metal—that is, the silver—contained in the buttons of lead obtained as the results of the foregoing operations, they are subjected to a purifying process by the metallurgist, called cupellation. By this means the lead and other impurities are driven off by heat in contact with a current of air, and the silver is left behind in a pure state. To perform this operation it is necessary to expose the buttons on some absorbing medium or porous support, and this support is commonly known as a cupel. No doubt many porous substances could be made available for the formation of cupels, but bone-ash is the best for all practical purposes, such as are required by the assayer. The bone-ash, in the condition of a very fine powder, is mixed with a little water in which has been dissolved a small quantity of potash, and moulded into the desired shape. The cupels are tightly consolidated by pressure in an iron mould of the form shown in [Fig. 7], which is the best in use, being well adapted for the manufacture of cupels. It consists of a slightly conical steel ring, 2 ins. in depth, and about 1½ in. in diameter at the top internally; a steel die with a wooden handle ([Fig. 8]) is made to fit the mould. To make a cupel the space in the ring is nearly filled with the moistened bone-ash, and pressed down by the hand, and afterwards by the die, the latter being driven into the ring by the application of a wooden mallet ([Fig. 9]) to the handle of the die. It will be seen from the illustration that the die forms a cavity in the cupel capable of receiving the charge of metal for assay. When the bone-ash has been sufficiently compressed, the die is withdrawn, and the cupel removed from the ring. This is a delicate operation, as sometimes the edges of the cupel are liable to be injured; to prevent which and facilitate the removal a loose plate of iron, exactly fitting the bottom of the mould, should be introduced previous to putting in the bone-ash. The iron plate of course being removed with the cupel, it must be replaced before another can be made. By introducing a cylindrical piece of wood to the lower aperture of the steel ring, the cupel can be removed without difficulty.

The size of the cupel should always be regulated according to the quantity of foreign matter to be absorbed, it being generally understood that the material of which it is formed takes up double its weight of lead. The process of cupelling is conducted in the furnace of the assayer, an apparatus of peculiar construction, the most important part of which, however, is the muffle ([Fig. 10]), consisting of a small arched oven of fire-clay closed at one end, and furnished with perpendicular slits in the sides, in order to allow of a free access of air to the cupels inside.

Fig. 10. Assayer’s Muffle for Cupels.

Fig. 11. Cupel Tongs.

Fig. 12. Cupels, section and perspective views.

The position of the muffle in the furnace is so arranged that it can be readily heated on every side; and when it has become red hot, six or eight cupels, previously well dried, are taken and placed on the floor of it, which should be covered with a thin layer of bone-ash. The form of tongs required for this purpose is shown in [Fig. 11]. When the cupels have been raised to the temperature of the muffle itself, the assays are put in by a very slender pair of tongs, the door of the furnace is then closed for a few minutes, when the metal will have become fused, and the litharge will begin to be taken up by the bone-ash of which the cupel is composed. The temperature of the furnace is now lowered as much as possible, although not to such an extent that it will retard the progress of oxidation and absorption. When nearly the whole of the lead has been thus absorbed, the bead remaining will have become very rich in silver, and, as the oxidation proceeds, will appear much agitated, assuming a rapid circular movement, and revolving with great rapidity. The silver gradually concentrates itself in the centre of the cupel, taking the form of a globule, and at this stage the fire should be made sharper, the operation being carefully watched. When the last particle of lead leaves the silver, the agitation will suddenly cease, and a beautiful phenomenon be witnessed, called by assayers the brightening. The button of silver then becomes brilliant and immovable, and the operation, when this takes place, is complete. The cupel must be cooled with very great care, in order to prevent the silver from sprouting; which if allowed to take place would result in considerable loss, besides destroying the accuracy of the assay. To prevent this sprouting it is a good plan immediately to cover the cupel by another, which has been heated for that purpose; the two are withdrawn together, and allowed to remain at the mouth of the muffle until the silver has become solid; the metal is then in a state of almost chemical purity, and may be detached and weighed. Previous to the latter, however, it should be carefully cleansed from all foreign matter, and flattened on a smooth-faced anvil, this process greatly assisting in the removal of any oxide of lead, which not unfrequently attaches itself to the globule of silver. The weighing is conducted with a pair of scales having an extremely delicate balance; and where any commercial transaction depends upon the accuracy of the assay, it is always imperative to make several tests of the same sample, to avoid the consequences of any accident or mistake.

The chief element in combination with silver on the large scale is lead. Formerly the plan adopted in the separation of this metal was cupellation alone. This process on the large scale is somewhat different from that just described; and as it may appear to the reader interesting and instructive, a brief explanation of it may not be considered out of place.

[CHAPTER IV.]

The Cupellation of Silver Ores.

This interesting process is performed in a reverberatory furnace of a very peculiar construction, the cupel employed on the large scale differing somewhat from the ordinary one, being considerably larger and varying also in form. It consists of a strong oval wrought-iron ring, with a part of the full shape omitted, as shown in accompanying sketch, in order to allow of the overflow of lead during the process, in the form of litharge. This iron ring, known as the test ring, contains the cupel, and in order to prepare the latter, the frame, which measures about 60 ins. in its longest diameter, 40 ins. in breadth, and 6 ins. in depth, is strengthened by having a number of broad strips of iron seamed across the bottom by riveting to the sides of it. The cupel itself is prepared for use by taking finely ground bone-ash, together with a little carbonate of potash, and working them up with just sufficient water to make the mass cohere properly; the carbonate of potash may be advantageously dissolved in the water; the latter is then applied in small quantities at a time to the bone-ash until the proper coherency has been obtained; of the total quantity of bone-ash employed in the operation, 2 per cent. of potash will be quantum sufficit to mix with it. The iron frame, or test, is then filled with the mixture, and it is pressed down into a solid compact mass, the centre part being hollowed out with a small trowel, the sides sloping towards the concavity in the middle; the hollow should not however be extended more than within 1 to 1½ in. of the bottom of the frame, and above the iron bars. The cupel forms the hearth of the furnace we have spoken of, and of which [Fig. 13] is a sectional view; it is removable, and not a fixture in the furnace. It must be left for several days to dry, after having been constructed as described, when it is ready for use, and only requires firmly wedging in its place beneath the arch of the furnace.

Fig. 13. Cupels, section and perspective views.

The fire should be only very moderate at the commencement of the operation, and the furnace slowly raised in temperature, lest the cupel should crack by being too quickly heated. As the temperature increases, if without any apparent defects in the bone-ash cupel, or hearth, which it may now be termed, the wind or blast, generally driven by a fan, is thrown in through a nozzle, or an aperture in the furnace, which, for facilitating the immediate removal of the bone-ash hearth, is placed upon an iron car, and runs beneath the vault of the furnace on rails, so that it may thus be very readily withdrawn when found necessary. The admission of a current of air into the furnace oxidizes the excess of lead, in combination with the silver, producing litharge on the surface of the molten mass; the formation of the litharge takes place rapidly, and it is continually blown forward by the strength of the blast as fast as it is produced, running through a gap or channel specially made for the purpose in the mouth of the cupel into a movable iron pot which is placed for its reception. The continual oxidization and flow-off of the lead alters the respective proportions of the metals in the cupel. For this reason it is always kept full of lead ore, which is effected by taking it in its fused state from a kettle in which it is ready melted by means of a long-handled ladle; and thus about 500 or 600 lbs. of metal are constantly kept in this bone-ash cupel or hearth.

As the silver necessarily increases in the hearth, it will require to be occasionally withdrawn, in order to make room for a further supply of lead ore. This process is adopted when it reaches about from 8 to 10 per cent. of silver to the ton (between 2,000 and 3,000 ozs.), and may be effectually performed by drilling a hole underneath the cupel, and letting the silver flow through it into a receptacle placed to receive it. Of course the operations of the furnace are arrested while these manipulations are being carried on. After the withdrawal of the silver, the hole is closed up again with a plug of moistened bone-ash prepared as before; when the process may be continued a second time by giving 500 or 600 lbs. of fresh lead ore to the cupel. Thus a single cupel will often last 48 hours, and 6 or 7 tons of lead may be oxidized upon it.

We have already observed that the prolongation of the cupelling process increases the richness of the remaining alloy, and this very rich silver-lead alloy is again subjected to a second operation in cupelling. This process of assaying or refining is similar in every respect to the former, and is often performed in the same furnace, the cupel being first of all brought to almost a bright red heat, when about 600 lbs. of the silver-lead alloy are added, and a strong current of air given in order to oxidize the remaining lead in combination with the silver. In this operation the material under treatment, previous to its introduction to the cupel, should be melted in a kettle easy of access, and added in its fused state. The current of air in connection with the heat of the furnace immediately begins to purify the silver by oxidizing the lead, and forms litharge, which passes off through the channel provided in the mouth of the cupel; as this proceeds, fresh silver-lead alloy is added, to keep the level of the metal always at the same height. This is continued until some three tons of the alloy from the first cupellation have been put in, and when about 600 or 700 lbs. of silver are collected in the cupel.

When the cupel has received the above proportion of metal, the addition of the alloy ceases, and the silver is allowed to purify. The litharge which passes off towards the close of this process will be richer in silver than in the former one; consequently it is found best in practical metallurgical operations to treat in a special manner the last part of silver cupelling on the large scale, for it needs very careful management indeed to secure all the silver, especially to do so in a fine state. Towards the completion of the process the fire should be increased considerably, in order to keep the silver thoroughly melted, and also to oxidize and completely remove every trace of lead that is possible. As it begins to purify itself from the remaining lead a characteristic brightness will be perceived. When this takes place the fire must be lowered, the wind or blast stopped, and the metal left to cool gradually. This latter proceeding is of some importance, as a too sudden cooling of the surface causes the interior of the metal to expand and shoot, by which means little globules of silver may be lost; therefore it should be allowed to cool very slowly.

The iron ring encircling the cupel with its contents may now be drawn from beneath the arch of the furnace, and the cake of silver taken from its bed in the bone-ash which formed the vessel, and cleaned of any impurity; when it may be re-melted in a plumbago crucible, and cast into ingot moulds. These moulds should be made of iron, and should always, when used for this purpose, be warmed and greased a little, previous to the introduction of the melted material, to prevent the metal from spitting and adhering to it. If skilfully treated during the process of cupellation, the desilvered lead seldom contains more than ·002 to ·003 per cent. of silver to the test assay of 200 grs., or between six and ten pennyweights to the ton, beyond which point it is unprofitable to carry on the operation.

The litharge which is formed and passes off during the process gradually grows richer in silver towards the end of the cupellation. It probably contains after concentration about thirty to forty ounces of silver to the ton of litharge. This is again subjected to the several operations of the same kind for the recovery of the silver.

It is somewhat remarkable that the present method of recovering and purifying this metal bears a strong resemblance to that employed in ancient times, and which is spoken of in the Holy Scriptures by the prophet Ezekiel (xxii. 18 and 20): “Son of man, the house of Israel is to me become dross: all they are brass, and tin, and iron, and lead, in the midst of the furnace; they are even the dross of silver.” And also, “As they gather silver, and brass, and iron, and lead, and tin, into the midst of the furnace, to blow the fire upon it, to melt it; so will I gather you in mine anger and in my fury, and I will leave you there, and melt you.” The celebrated metallurgist Dr. Lamborn says, “Only those who have seen, beneath the glowing arch at the smelting works, flames surging wave after wave across the surface of the liquid metal, carrying all the substances, here called dross, from the pure silver; and only those who have heard the roar of the fiery blast, that ceases neither day nor night, until its task of purification is accomplished,—can appreciate the terrible force of the figure made use of by the prophet.” According to the above scriptural passage it is evident that the ancients were in possession of the first rudiments of assaying, and understood to some extent the purification of metals; but scriptural testimony does not point out with what amount of skill and success these operations were performed. Judging from the appliances which have been handed down from generation to generation, we are inclined to think they must have been practised somewhat rudely; for it has been left to the present school of scientific and practical metallurgists to found and develop the art in the direction of that commercial success to which it has at the present day attained.

This plan of cupellation which we have just described is still adopted in many continental works in the assaying of silver-lead ores. In England the system has been almost entirely superseded by one invented by the late Mr. Pattinson of Newcastle, and which is confidently stated to be far more convenient in practice.

[CHAPTER V.]

The Alloys of Silver.

Fine silver enters freely into combination with nearly all the useful metals, but its most important alloys are those prepared from copper, the latter substance being more suitable for the production of silversmith’s work than any other; whilst it produces a more pleasing effect, if not over-alloyed, in regard to finish. Silver articles, especially of the filigree kinds, if the designs are good, possess a very tasteful appearance. In treating of the alloys of silver, it is our intention, first, to give a cursory glance at the chemical and physical properties of the metals which form these alloys. Such a description, although brief, will, we believe, prove of essential service, not only to working silversmiths and metalsmiths, but also to goldsmiths and jewellers, who are constantly manipulating with these inferior metals in precisely the same way as the silversmith. Besides, such information cannot, we apprehend, fail to be useful, whether to the student, the theorist, or the practical worker.

An alloy is the union of two or more metals by fusion, so as to form a metallic compound. It may consist of any number of the metallic elements, and in any proportion, provided they will chemically combine, always excepting mercury as one of the ingredients. In this latter case the mixture is called an amalgam. Chemistry has made us acquainted with about forty-nine metals; of that number, however, not more than fourteen are employed to any considerable extent for industrial art purposes. They are as follow: Gold, silver, copper, zinc, platinum, aluminum, nickel, iron, mercury, lead, tin, arsenic, antimony, and bismuth. Some of these are occasionally employed for special purposes in the arts in their pure state; but where hardness is to be a distinguishing characteristic, combined with certain variations in shades of colour, a union is effected of two or more of these metals in different proportions, by fusion and stirring, so as to form the requisite alloy. Metals used in the pure state, that is, without any mixture of alloy, have very few applications in regard to industrial pursuits and the arts. The precious metals—gold, silver, &c.—would be much too soft, while, on the other hand, arsenic, bismuth, and antimony would be far too brittle to be employed alone for manufacturing purposes. It is quite possible to effect some thousands of alloys, but there do not appear to have been more than about three hundred practised successfully for commercial purposes.

The principal alloy of silver, as we have already remarked, is copper; but, occasionally, nickel, and even zinc are employed in the case of the commoner qualities of silver. Tin is also used in the preparation of solder for these qualities, in order to render it the more easy of fusion when used for soldering the work. Of the distinctive features of these elements of silver-alloy we shall now speak with some amount of detail.

Silver will unite with copper in various proportions by melting the two ingredients together, and stirring them whilst in a fused state. A product will thus be formed differing physically in character from fine silver, caused by the loss of some little of the latter’s ductility and malleability; but, on the other hand, a compound will be produced harder and more elastic, which is in every sense better adapted to the manufacture and also to the durability of the articles made by the silversmith.

Copper, like the precious metals, appears to have been known from a very early age, being one of the six metals spoken of in the Old Testament; and described by the historian as being also one of the seven made use of by the ancient philosopher. It is of a reddish colour, malleable, ductile, and tenacious. It is largely employed in alloying both gold and silver for the manufacture of jewellery and other articles. With regard to malleability, it stands next to gold and silver in the list of useful metals; in ductility it occupies the fifth position; and in tenacity one only is superior, viz. iron. It is not very fixed in the fire, for if subjected to a long-continued heat it loses a part of its substance; for this reason the alloys of silver and copper should be carefully watched in the crucible to prevent this loss when under the action of the fire.

When struck copper gives only a feeble sound, and is easily abraded by the file. It fuses at a good white heat, or about 1994° Fahr., although some authors have given it as 1996° Fahr. Its specific gravity varies between 8·88 for cast copper, and 8·96 when rolled and hammered. It loses between one-eighth and one-ninth, or 4/35ths, of its weight in water. When exposed to a damp atmosphere a greenish oxide, called verdigris, is produced on its surface, and this is one of the reasons why silver articles containing a percentage of copper become so readily discoloured if left exposed to atmospheric influences; copper also, if heated in contact with the air, quickly becomes oxidized, and, on being touched, scales fall off: these form the protoxide of copper. If this process is frequently repeated under a great heat, each time the metal is operated upon it loses a part of its malleability and ductility, which are both eminent characteristics of the pure metal. Most of the ordinary acids act on copper but slowly in the cold, but nitric acid very readily dissolves it, even if largely diluted. Copper amalgamates with most of the metals, and its subsidiary alloys are very largely employed in the arts and manufactures of every kind.

The bean-shot copper of commerce, costing about a shilling per pound avoirdupois weight, is quite good enough for all the practical purposes of the silversmith.

Fig. 14. Venus. Egyptian Mark for Copper.

The name given to this metal by the alchemists was Venus ([Fig. 14]), which is one of the principal planets, whose orbit is situated between the Earth and Mercury. The scientific name of cuprum for copper is derived from the Isle of Cyprus, where, it is said by Pliny, the Greeks discovered the method of mining and working it. Copper is found distributed all over the world; a considerable portion, however, is found in the United Kingdom.

Nickel.—This metal is found chiefly in the Hartz Mountains. It was formerly called by the Germans “Kupfer nickel,” or false copper, “nickel” being a term of detraction. It was first discovered about a century and a half ago by Cronstedt. It has a greyish-white colour, and is slightly magnetic, i.e. it is attracted by the magnet in the same way as iron and steel, but it loses this property if heated to about 600° Fahr. Its specific gravity varies between 8·40 and 8·50, according to the amount of compression it has received, and it is rather brittle; it may, however, be drawn into wire, and rolled flat, or into sheets. It is considerably harder and less ductile than any of the other metals employed in jeweller’s and silversmith’s work. In hardness it nearly approaches iron, and on this account, when polished, a characteristic brightness is produced. The malleability of nickel is less than that of iron, standing tenth in the list of useful metals; and in ductility it also occupies the tenth position. Nickel is very infusible, and does not so easily oxidize or tarnish at ordinary temperatures as copper does. Several countries have tried to employ it in the manufacture of small coin for the currency, but its use has now been almost abandoned.

Nickel alloys are much used in the arts for manufacturing purposes, under the name of “German silver,” there being large demand for this metal, as it forms the hard white alloy much used in making “electro-plate,” and on which silver is afterwards deposited. It also is used in common silver alloys, in order to keep up the whiteness of the latter element, the addition of too large a proportion of copper maintaining the tint of the latter metal, in too strong a degree to be altogether employed by the silver-worker. Nickel is sometimes specially employed, in combination with other metals, to replace or imitate silver in the manufacture of commercial wares, while with copper, zinc, tin, &c., it forms very useful alloys, producing great hardness.

Zinc.—This metal in its pure state is sometimes called spelter. At the present day it is not much used for alloying silver; but, as it is commonly employed in the preparation of silver-solder, it is necessary that the amateur and the student should know, as well as the practical mechanic, the distinctive characteristics of it, together with the qualities it imparts to others when in combination with them. As a metallic substance it was unknown until a long time subsequent to the discovery of the principal metals; and only since the commencement of the present century has its uses been thoroughly known and appreciated in the industrial world. In its pure state, zinc is a bluish-white metal, hard and highly crystalline; but, when raised to a heat of between 250° and 300° Fahr., it is malleable, and may safely be rolled and hammered: it is in this way that the zinc of commerce is produced.

Zinc may be annealed by placing it for a time in boiling water. Its specific gravity varies between 6·8 and 7·2, according to the previous kind of mechanical treatment it has received. At 773° Fahr. it melts, and is quickly oxidized by exposure to a current of air, emitting white vapours, which rise into the air, and are not unlike cotton-flakes; oxide of zinc is thus formed by the burning away of the zinc. Spelter or zinc is employed by jewellers in the manufacture of bright gold alloys, as it gives liveliness of colour to their wares not to be equalled by any other metal. (For the proportions and treatment of this composition see “The Goldsmith’s Handbook.”) It may be alloyed with most of the metals we have named; its uses in roofing, gutters, spouting, and chimney-pots being all well known. All the acids very readily attack it in the gold, and even when largely diluted; it speedily tarnishes, and becomes covered with a white oxide which protects the metal from atmospheric influences. In point of malleability zinc stands eighth among the metals, seventh in ductility, and as regards tenacity about seventh also. In chemistry it is represented by the symbol Zn. Its value when in a state of purity, commercially speaking, is about 4d. per. lb.

Tin.—This appears to have been one of the oldest known metals, and was employed in the Egyptian arts by the ancients, in combination with copper. Its colour is white, with a shining lustre almost as brilliant as that of silver, but it tarnishes much more quickly than alloys of the latter metal. With the exception of aluminum and zinc, it is the lightest of all the metals, its density being between 7·0 and 7·3, whether cast, hammered, or rolled. It is found in abundance in Cornwall, where it was also obtained at a very early period by the Phœnicians; and it is reported in Soame’s “Latin Church,” p. 30, that it was through the medium of the trade in tin that Christianity was first introduced into this country. Tin is not of a fixed nature like gold or silver, but melts in a moderate fire long before it becomes red hot, or about 442° Fahr. It is rapidly oxidized when kept for a long time in a fire having a free access to the air; and it is dissolved by hydrochloric, sulphuric, and nitric acids, the latter acting on it most powerfully. Tin should not be alloyed with gold or silver, as with either of these it easily enters into combination by fusion, rendering them extremely brittle, especially in the case of silver, which becomes by the least mixture of it so brittle that it is totally unfit for the work of the silversmith. However, for solder, for filing into dust, it may be advantageously employed to promote a quicker fusion; but even for this it should be avoided where it is possible to do so. The vapours of tin are also permanently injurious in the melting of gold, silver, and their alloys, as they render them very unworkable, and the operator being often at a loss to understand the cause of his misfortune; therefore, in melting silver alloys, it is advisable to avoid as much as possible the introduction of little bits of scrap tin into the furnace. If such a thing should happen, however, make the fire once or twice stronger in order that the tin may all be destroyed before the crucible containing the silver alloy is put in.

Fig. 15. Jupiter. Egyptian mark for Tin.

Tin is very malleable, moderately ductile, and tenacious, being fifth on the list for malleability, eighth for ductility, and eighth for tenacity. The Egyptian mark or symbol for tin (sign of “Jupiter”) was the same as is represented in [Fig. 15], and related to the planet of that name, one remarkable for its brightness. In mythology it is understood as representing the supreme deity of the Greeks and Romans. The modern scientific name for tin is Sn. Tin loses over one-seventh, or 4/29ths, of its weight in water from its absolute weight in air. In the next chapter we shall treat of the mixing of silver alloys, &c., and in order to make our information regarding the various metals so employed as complete as possible, we shall conclude this one with the following tables, each of which will no doubt be found useful:—

Table of Metallic Elements.

Melting-points of the Principal Metals.

Physical Properties of the Principal Metals.

[A] The above weights were lbs. sustained by 0·787 of a line in diameter, in wires of the various metals.

[CHAPTER VI.][A]

Various Qualities of Silver.

[A] See observations on Depreciation of Cost Price of Silver in Preface to Fourth Edition (pp. vii, viii), and the new Table of Cost Prices of Alloys in this Chapter, following the Preface (p. ix).

The chemical and physical properties of fine silver having been dealt with in a preceding chapter, we shall not refer to them again in detail; but, as we have already observed that it is sometimes employed in its pure state for special purposes, it is desirable that we should point out the uses to which it has been applied, especially those of a mechanical nature. With reference to the latter part of the subject we will now proceed to describe the commercial utility of the metal.

One of the greatest demands for pure silver—if not the greatest of all—is in the manufacture of fine filigree work, a branch of industry extensively practised on the Continent. This kind of silversmith’s work was attempted to be revived in this country during the years 1864-5, Birmingham and London being the principal places where the manufacture was carried on; but the success of the undertaking as a staple industry must, at the most, have been only a partial one, for it soon declined, and the trade was thus virtually left, as before, in the hands of our Eastern competitors; most of whom produce splendid specimens of the art of filigree and fine wire-working. In India this work is wonderfully performed, and it is truly marvellous to witness the beautiful handiwork of the natives who practise this craft. Their productions are quite the work of the true artist, almost every article representing Nature in some of her various forms, such as flowers, animals, serpents, &c., and these are so skilfully imitated that no one could possibly dispute either the faithfulness of the representation or the ability of the workman. This is all the more surprising, because in India the natives have not the modern mechanical appliances which we possess in this country. The jeweller there represents to some extent our travelling tinker, only with this difference, that the travelling tinker in this country is generally an inexperienced and unskilful workman, whereas the Indian, if we are to judge him by his work, must be just the reverse.

Filigree wire-work is manufactured in Italy, Germany, Norway, and Sweden, and the secret of these countries maintaining the monopoly in this branch of the silversmith’s trade is that labour there is cheap; and not in any sense because English workmen cannot make the articles in question. It is owing to this cheapness of labour and the inexpensiveness of living that our Continental competitors can beat us by underselling us in the market; and to no other cause can the production of the foreign cheap article be assigned.

In India the art of working in silver and gold has long been practised, and so particular are the workmen there about the absolute purity of the metals they use, that they refine them by melting five times, under a very strong blast heat, before commencing the work of manufacture. The principal places where these art-manufactures are carried on are in Southern India and at Trichinopoly; and in these districts the delicacy and intricacy of the workmanship are brought to the greatest possible perfection. The articles produced there are all “hand-made,” and wrought entirely with a few simple tools, such as a hammer and an anvil (both of which are highly polished and burnished), a few fine pliers, blow-pipes, burnishers, scrapers, a pair of fine dividers, and some delicate scales and weights; these, with a few perforated steel-plates for drawing the wire through, comprise the chief appliances of the travelling native jewellers. The process of the work is very simple. It is commenced by hammering out the metal upon the anvil, and when it has assumed a certain degree of thinness the dividers are next brought into requisition to mark it into certain widths, which are subsequently cut into strips and drawn into very fine wire through perforated steel-plates, a pair of strong pliers being used for the purpose. The holes in the steel-plates consist of graduated sizes, and by this means the strips of metal are soon considerably reduced; and when the proper thinness has been attained the wire is ready for the exercise of the practical skill and dexterity of the artisan, who produces from it the best filigree work in the world. Most of the native jewellers have books containing a variety of designs, but they more commonly work from memory, without any reference to patterns.

The principal localities where this description of work is produced in the highest perfection are Delhi, Cuttack, and Trichinopoly, in India; and Genoa, Paris, Florence, Malta, Norway, and Sweden. The Indian filigree work is the finest and cheapest in the world. The Maltese manufacture a very good kind, and their crosses are much admired; so also do the Chinese and Japanese, but the manufactures of these latter countries are not so tasteful as those of India, consequently they have not been so highly appreciated. Norway and Sweden produce filigree work of a very light weight; but still their productions in this art will not compare in regard to effect with the finest specimens from India.

We have said that the silver employed by the filigree worker should be in every case absolutely pure; because, when it is quite fine, it is extremely soft and pliable, so that it will remain in almost any form the artist may choose to work it, without that springiness which is found in all alloyed metals. However small might be the amount of alloy contained in the metal, the least admixture of it would produce an elasticity in the wire when pressed into form which would make it unworkable for fine filigree purposes; and in this state it would be the utter bane of the workman, as his progress would be altogether impeded in the production of his work. It is of the greatest importance that the spirals, and all the various forms required in filigree working, should remain steadily in their places when pressed into shape, without that rebounding which happens in the case of metals of an elastic nature, and in consequence of which no really first-class work can be performed in connection with this art. For such reasons as these it will be at once palpable even to the ordinary reader that fine silver should always be used in preference to alloyed in the manufacture of filigree work.

The various ornaments of the filigree kind are commonly enclosed in a rim of plain and somewhat stronger wire, which gives additional strength to each part; and, when put together, tends to compose an article of considerably greater durability. In England these outside rims consist exclusively of sterling or standard silver, whilst all the inner work is of the finer material.

There are several methods of preparing the wire called “filigree.” The oldest and the one almost invariably practised in India consists in the first place in drawing down the wire in a circular form until the very lowest possible thinness has been attained, and frequently annealing it during the process, which is done by heating it to a red heat in a muffle placed upon an iron or copper pan. When this process has been effectually performed the wire is taken (if of the proper degree of thinness) and doubled together; these two fine wires are then twisted into one cord, which should be of the fineness desired. The wire requires annealing more than once during the process of twisting, and when it is completed it has a corded appearance, it is then ready for the manufacture of the various articles comprised in this kind of work.

The old plan of twisting was accomplished in the following manner. One end of the doubled wire being firmly secured in a vice or some other suitable instrument, so as to prevent it from turning round and so prevent the progress of the work, the other end of it was also firmly secured in a small hand machine or vice, which was made to revolve by turning a small handle with the right hand, the machine being held and regulated with the left, in order to keep the wire out at its full length so as to avoid knotting in the various parts of it; it was in this manner that fine filigree wire was in the first instance made.

The second plan was somewhat different, and in regard to the last part of the process it was certainly a great advantage, especially in the saving of labour, as a greater quantity could be prepared in a much less time than by the old method, that being slow in its progress. Here the lathe was made to supply the place of the small hand machine, the speed of which soon brought about the object in view.

The flattening of this twisted wire has now commonly come into use, and is effected by passing it through small steel rollers, hardened and polished. The object of this is soon manifest, as the labour-saving process is brought prominently into play: the wire in the first place need not be so finely drawn, and secondly the same filigree surface can be made to appear upon the articles as before, by securing the edges of the wires which show the filigree uppermost; and this is always the case in manipulating with this kind of wire. This method is generally in vogue with most filigree workers.

A third plan of preparing the material for the manufacture of filigree work is, we believe, due to the ingenuity of a celebrated Birmingham firm, who extensively practised this kind of work some years ago. The secret is not now generally known to the trade, therefore a few observations bearing upon it will not be unacceptable to those for whose benefit we are writing. The process is commenced in the same manner as before, in the preparation of the round wire, though this need not be drawn so fine, because by this method we have no twisting. When the round wire has arrived at the proper size it is flattened in the manner already explained; and when this is done it should be annealed, but experience will dictate best when this particular process should be carried out. After this latter operation the wire is submitted to the action of very small rollers, and bearing the pattern required in small grooves of various sizes. The pattern takes effect upon the edges of the wires only, and resembles the milled or serrated edges of our coinage, only of course the latter bears no comparison with regard to fineness. Lastly, the wire is again passed through the flattening rollers, and then it is ready to be worked up into the object desired.

Having gone through the general details of filigree working we shall next direct our attention to the component parts and commercial uses of the English standards, together with those of some other countries. In England there are two silver standards, called respectively the old and the new standards. They are as follows:—

Fine silver per lb. troy.

The older of these appears to have been always the legally recognised standard for the coinage, and also for the manufacture of plate. By a law passed, however, in the reign of William III. (1697) it was raised to 11 oz. 10 dwts. of fine silver in the pound troy weight. The manufacture of silver articles from this standard was soon found to be not so durable as those made under the older one; consequently the silversmiths were permitted by a law passed in the reign of George III. (1819) to manufacture from the former standard of 11 oz. 2 dwts., the use of the new one being likewise permitted for the benefit of those who chose to avail themselves of it; and to this day it remains an English standard, though hardly ever employed.

By the Silver Coinage Act (10 Geo. 5), the fineness of the British coinage was reduced on account of the increased price of silver bullion; and the silver coinage now consists of one-half silver, one-half alloy, one troy pound of silver being coined into sixty-six shillings. The copper which composes the alloy in the silver coinage hardens the material employed, and it is found to wear better.

In order to make the matter as simple as possible, we purpose giving a few practical alloys, as follows:—

Old standard silver alloy, cost 4s. 4d. per oz.

If it is intended that the above alloy should be for Hall-marking, it will be advisable to add a little extra silver to the prepared composition, because fine silver purchased from the refiner or bullion dealer is never absolutely pure, consequently the work will not pass the Hall; or better still alloy as follows:—

Old standard silver for Hall marking.

The new standard silver is composed of 38-1/3-40ths of fine silver and 1-2/3-40ths of copper alloy; or millesimal fineness 959 parts of fine silver and 41 parts of copper per 1,000 parts; the remedy being as before 0·004 parts.

New standard silver alloy, cost 4s. 6d. per oz.

New standard silver for Hall marking.

Quality commonly used in England.

The qualities of the silver employed by the English silversmiths are invariably below the standard, the duties, assay charges, and loss of time in sending the work to the Hall to be marked acting as a great drawback to the trade in the midst of the keen competition of the present day. Silver chains, brooches, buckles, collarets, &c. are for the most part manufactured from inferior metal. In fact, some manufacturers positively refuse to make Hall-marked goods, on account of the great drawbacks attending the marking.

The alloys of silver are not calculated on the carat system, like gold, but by certain numbers, or other distinctive features, well understood by the particular firms which trade in silver wares. For our present purpose it will be sufficient to distinguish them by using the numerals, 1, 2, 3, 4, &c.; the alloy nearest approaching sterling or standard we shall call No. 1, and so on downwards until the lowest quality has been reached. We may state that silver does not lose its whiteness if not alloyed below equal quantities of the two metals; however, the alloys used in manufactures seldom reach so low a limit.

Silver alloy No. 1, cost 4s. 2d. per oz.