Hard solders—Composition of gold solders—Silver solders—Spelter solders for copper, brass and iron—Moulds for casting solder. 

Soldering is the art of joining together separate pieces of metal by running between them some other metal or alloy, which will closely adhere to their surfaces and bind them together. The metal or alloy used for this purpose is known as solder. It must have a lower melting point— require less heat to melt it—than the metal of which the work is composed, so that a temperature high enough to melt the solder will leave the work uninjured. But the melting point of the solder should approach as nearly as may be conveniently possible to that of the work, for a more perfect and a stronger joint is thus produced. " The essence of true soldering," says Mr. Hiorns, " is that there should be a certain amount of interfusion or alloying be tween the solder and the metal to be soldered, an intimate union of the two thus taking place." 
There are many kinds of solder. They are known by such names as gold solder, silver solder, spelter, tinman's and plumber's solder. But they may be broadly divided into two groups—hard solders and soft solders. Hard solders melt at, or above, red heat, and are used for materials which can safely withstand such temperatures. But soft solders require comparatively little heat to fuse them, so they can be used for soldering almost any metal or alloy. Joints made with hard solder are considerably stronger than those made with soft. The harder solders are used generally by goldsmiths, jewellers and silversmiths; the softer kinds by plumbers and tinsmiths. Coppersmiths use both, and, sad to relate, even goldsmiths occasionally use " soft tommy." It is impossible, without doing serious damage, to use hard solder on work upon which there is already any soft. 

Before discussing the solders employed for goldwork, a few words are necessary as to the method by which the proportion of pure gold in any article is indicated. The quality of gold is expressed by the number of parts of pure gold out of 24 parts or carats. Thus pure or " fine " gold is 24 carat. If any other metal is mixed with the gold, the latter is said to be alloyed by it. For instance, 22 carat gold contains 22 parts of fine gold and 2 parts of some other metal or metals; 18 carat gold has 18 parts of pure gold to 6 parts of alloy, and so on. Gold coinage in England con sists of 22 parts of fine gold and 2 parts of copper, or, in thousandth parts, 916-66 parts of pure gold to 83'34 parts of copper. This is known as " Standard " gold. The metals generally used to alloy gold for manufacturing purposes are copper and silver. The addition of any portion of these metals to a piece of gold lowers its melting point. Less heat is required to fuse it. The greater the amount of alloy added, the lower is the melting point of the mixture. It will be obvious then that the quality of the gold, whether fine or 22, 20, 18, 15, 12 or any other carat, is a clear indica tion as to its relative melting point. So, any gold may be used as a solder for a better quality gold. Thus 12 carat gold will act as a solder for 15 carat or any better quality; 16 carat for 18 or better; 18 carat for 20, 20 carat for 22 or for fine gold, and so on. But it would be, of course, impossible to solder a piece of 15 carat work with 18 carat gold; the Avork would melt first. 

To make a solder for gold, it is only necessary to add a small portion (a fourth, fifth or sixth part by weight) of copper, or of copper and silver, to a piece of the gold which you are to use. If a small amount is required, melt them together on the charcoal till they are thoroughly mixed. Flatten out the little bead of molten metal as it begins to cool. Drop it in pickle and afterwards roll or hammer it out to about size 6 on the metal gauge. A larger amount is best melted in a crucible, cast in a flat sheet a,nd rolled out to the thickness required. For example, you are using 18 carat gold. A pennyweight of it contains 18 grains of fine gold and 6 grains of alloy. If you added 3 grains more •of alloy then you would have 18 grains of gold and 9 grains of alloy,—two-thirds gold, one-third alloy. Now two-thirds of 24 (carats) is 16, so the mixture would be 16 carat in quality. To use 16 carat solder on 18 carat gold is not unusual, but it requires some experience, as their melting points are not so very far apart. To make an easier solder, add 5 grains of alloy instead of 3 grains, to the pennyweight of 18 carat gold. The resulting mixture will be just under 15 carat, and will prove a perfectly safe solder to use on 18 carat gold. In a similar manner the proportion of alloy to be added to produce a solder of any quality may be reckoned out. 

It should be remembered that with copper as the alloy, you produce a solder which is richer in colour than one alloyed with silver, but it will not flow quite so easily. So, as a rule, both metals are used together, as in the examples given below, which are for solders made from fine gold. Always choose a solder which is as good as you can safely 
use on the work. 

Gold Solders 
Fine Gold. Silver. Copper. Total. Quality of the Solder. 
No. dwt. gr. dwt. gr. dwt. gr. dwt. gr. 
1. 
1 0 0 9 0 6 1 15 Justover 15carat. 

2. 
1 0 012 012 2 0 12oarat. 

3. 
10 o m 0 10.',-2 3 Under 12 oarat. 

4. 
1 0 0 17 0 14 2 7 JustunderlOicarat. 

5. 
1 0 0 19i 0 15 210J Under10oarat, 

and lower qualities on the same principle. 

Pure silver is known as " fine " silver, but it is too soft for general use. It is, therefore, alloyed with copper. 
The proportion of alloy in what is known as " Standard " silver,orthesilverusedforcoinage,is 18partsalloy(copper) to 222partsof finesilver;or,inthousandthparts,Standard silver contains 925 parts of fine silver to 75 parts of alloy; or 37 fortieths of fine silver; or, 11 oz. 2 dwt. of fine silver to 18 dwt. of copper. This is the standard quality for " Sterling silver," and is "Hall-marked" as such. There is another standard, known as the " New Sterling " or " Britannia " standard, in which the proportions are 10 parts alloy to 230 parts fine silver, or 959 thousandths fine silver, or 11 oz. 10 dwt. fine silver to 10 dwt. of alloy. But this alloy does not wear very well, so it is comparatively little used. 

Silver solders are usually made by alloying silver with copper or with brass (i. e. copper and zinc). Those alloyed with copper alone are harder and do not flow along the joint quite so freely as those solders of which zinc is an ingredient. On the other hand solders which contain much zinc are not quite so strong as those made from silver and copper alone, and if heated many times, the zinc which happens to be near the surface is burnt away—leaving the surfacerough. Thismaycausetroubleinfinishing. Solders for work which is to be enamelled, should therefore contain little or no zinc. But for ordinary silverwork, where the ease with which a solder will flow is an important considera tion, the solder may contain a fair percentage of zinc. The first solder given below is very hard, and, on account of its freedom from zinc, suitable for work which has to be enamelled. The second is extremely strong and flows quite easily. It is more expensive than the third, owing to the greater proportion of silver in it. Brass wire is used as the alloy, not scrap brass, because wire, sold commercially, is of pretty good quality, while sheet brass may not be. The composition of good brass wire is about 70% copper and 30% zinc. The third solder flows very easily indeed, but it is not so strong as the others. And, if made from pins, the difficulty of the burning out of the zinc may arise. Pins may contain from 55 to 70% of zinc. 

Silver Solders 
No. 1. Silver 4 parts, copper 1 part. Very hard. 
No. 2. Silver 3 parts, brass wire 1 part. Good and strong, 
No. 3. Silver 2 parts, brass wire or good pins 1 part. Easy flowing. 


These silver solders are also used on copper and brass. 

Solders for copper, brass or iron, are often known as spelter, and the process of soldering as brazing. The solder generally used is a kind of brass—made from copper and zinc. The melting point of the alloy depends upon the percentage of zinc present, so that as the proportion of zinc increases, the melting point is lowered. Occasionally small percentages of tin and lead are included, but these metals, though lowering the melting point, yet weaken the alloy, so they should bo avoided. Hiorns gives the following :— 
No. Copper. Zinc. Tin. Lead. Colour. Remarks. 
.
1. 58 42 Reddish yellow Very strong. 
——
2. 53 47 Do. Strong. 
——
3.48 
52 Do. Medium. 
4. 
54£ 43i li 1 Do. Do. 
——
5. 34 66 White Easily fusible. 
6.44 
50 4 2 Grey Do. 


7. 
57 28 15 4 White White solder. 

The alloy generally used contains equal parts of copper and zinc; while a very fusible solder can be made from two parts of zinc to one of copper. A solder to use with any brass can be made by taking a portion of the brass and adding to it a quarter of its weight in zinc. The best method of making brass solder is to melt the brass or copper first under a layer of charcoal. Warm the zinc to near its melting point and add it to the brass. Use common table salt, pearlash or cream of tartar as a flux. They are better than borax for this purpose. Stir the alloy well before pouring. The solder may be poured from a height into water, passing through a wet broom on its way, to break it into small pieces. Or it may be pounded into powder in an iron mortar immediately it has cooled sufficiently to set. It is a mistake to remelt any hard solder containing zinc for the purpose of obtaining a more regular mixing of the ingredients. Some of the zinc is burnt out each time the alloy is heated, so the fusibility of the solder is impaired, not improved. 

The ingredients for gold and silver solders, with the exception given below, are, when melted, poured into what are known as ingot moulds. These moulds are made in various forms. That shown in Fig. 2 is suitable for casting rectangular pieces of solder or of the metal itself. These plates or ingots may be rolled out afterwards into long strips if required. This type of mould consists of two iron plates, kept apart by a flange the thickness of the ingot required. By sliding one plate over the other the shape of the mould may be varied. The two plates are kept together by a clamp. Another convenient form of ingot mould is shown in Fig. 3. It is made from two pieces of sheet iron. The flange between them is, in this case, formed from a piece of iron wire which has been flattened by passing it through the rolls. The wire is then bent to the shape of the ingot required, in this case that of a capital U, perhaps 3 inches high, with the top ends bent out a little; in thickness rather less than ^ inch. By varying the shape and thick ness of the bent iron wire, ingots of any form or thickness may be cast, Figs. 4 and 5. A few nicks made with a 3-square file across the flat sides of the wire will assist the escape of the air when the metal is poured in. The bent iron wire and the two plates are firmly held together by U-shaped pieces of stout iron wire slid on at intervals round the edge of the plates, Fig. 6. The mould used by jewellers for casting ingots is made from a piece of hearthstone— the white stone used for cleaning hearths. A block of this is taken and rubbed quite flat on each side. On one face a hollow is carved to the shape of the ingot required, see Fig. 7. The wide-open mouth or " pour " at A is the way the metal is to come in. The opening is made wider here so that none gets spilt outside. Then with a 3-square file, make a number of shallow grooves across the face of the mould to let the air out. Bake dry. Take a slab of charcoal and rub one side of it quite flat on a stone. Neat one end of this flattened side dig a little pit large enough to hold the metal when melted. If you now put the piece of hearthstone with the side which has been hollowed out against the flat part of the charcoal you have a complete mould, with only the little opening or " pour " turned so as to be quite close to the little pit in the charcoal. The two parts of the mould—hearthstone and charcoal, may be tied together with wire, Fig. 8. When the metal is melted, and this is done in the hollow on the charcoal, you have only to tilt the mould so that the molten metal may run into the place prepared for it. These hearthstone moulds may be made in any shape. For wire make them long and narrow, tapering to a point at the end away from the pour. This point is for convenience in getting it through the holes in the drawplate. It saves filing or hammering. 

The mould having been prepared, take the ingredients for your solder, cut them into small pieces and put them into a fire-clay crucible, with a little powdered borax'on top. Put the crucible in the furnace, or on to a place prepared for it on the hearth. Heat it until all its contents have melted. If you are using a metal mould, warm it well by placing it on the furnace or hearth. Just before you are ready to pour the metal, put a little sweet oil into the mould, to grease it. Stir the molten metal well with an iron rod. Some of the borax may stick to the rod, but don't, if you can help it, pick up any of the metal. Then lift the crucible with the tongs and steadily fill the mould. Avoid splashing the metal in. Put the crucible back in the furnace if there is any metal yet remaining in it. The metalinthe mouldwillbesetinhalfa minute. Theclamps may be knocked off, the metal turned out, and the mould got ready at once for the remainder. Be careful that there is not a trace of moisture about the mould when you pour the metal into it, for it would blow up, with possibly serious results. The oil does not matter. Some borax will have collected at the top of the ingot. A sharp blow may bring it off, or the ingot may be scraped clean or boiled in pickle. Then carefully cut and file off any rough edges or stray branches that may be present on the ingot; for if you use an ingot the edges of which are rough and uneven, with thin projecting pieces, for rolling into sheet or drawing into wire, cracks will be sure to appear in it. Roll out your ingot of solder to a convenient thickness, say size 8 on the metal gauge, or thinner for very small work. 

The exception to the use of ingot moulds, referred to on page 11, is that in which you wish to make a very small piece of solder. You may melt it on a charcoal block. It will run up into a ball. Flatten this as it cools by pressing any piece of iron on to it. Then hammer it out as required. 

That a piece of solder shall never be mistaken for a piece of silver, or vice versa, it is a good plan to scratch a number of lines in all directions across the sheet of solder when it has been rolled to the required thickness. If this is done it can never afterwards be mistaken for sheet silver. 

We have now come to the end of the hard solders. But before going on to the soft solders, we will discuss the manner in which the former are used in actual practice. But first it may be well to repeat the warning against the use of hard solder on any article on which there is already any trace of soft solder.