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

CHAPTER V.

Chapter 222,484 wordsPublic domain

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.

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 4_d._ 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 Ph[oe]nicians; 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.

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.

+-----------------------+----------+---------------------+ | Names of Elements. | Symbols. | Specific Gravities. | +-----------------------+----------+---------------------| | Platinum | Pt | 21·40 to 21·50 | | Gold | Au | 19·25 " 19·50 | | Mercury | Hg | 13·56 " 13·59 | | Lead | Pb | 11·40 " 11·45 | | Silver | Ag | 10·47 " 10·50 | | Bismuth | Bi | 9·82 " 9·90 | | Copper | Cu | 8·89 " 8·96 | | Nickel | Ni | 8·50 " 8·60 | | Iron | Fe | 7·77 " 7·80 | | Tin | Sn | 7·25 " 7·30 | | Zinc | Zn | 6·80 " 7·20 | | Antimony | Sb | 6·75 " 6·80 | | Arsenic | As | 5·70 " 5·90 | | Aluminum | Al | 2·56 " 2·60 | +-----------------------+----------+---------------------+

Melting-points of the Principal Metals.

+--------------------+--------------+-----------------+ | Names of Elements. | Fahrenheit. | Centigrade. | +--------------------+--------------+-----------------+ | Platinum | { Infusible, except by the | | | { oxyhydrogen blow-pipe. | | Cast Iron | 2786° | 1530° | | Nickel | 2700° | 1482° | | Gold | 2016° | 1102° | | Copper | 1994° | 1090° | | Silver | 1873° | 1023° | | Aluminum | 1300° | 705° | | Zinc | 773° | 412° | | Lead | 612° | 322° | | Bismuth | 497° | 258° | | Tin | 442° | 228° | | Antimony | Fuses a little below red heat. | | Arsenic | Volatilises before it fuses. | +--------------------+--------------------------------+

Physical Properties of the Principal Metals.

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