Gold, both pure and variously alloyed, is used to a considerable extent in soldering, but on account of its expensiveness it is limited to articles made of gold or platinum, or the most delicate small steel objects.

Gold alloys are of different colors, according to the kind and proportion of the other metals used. There are yellow, red, white, and green gold alloys. The color of the special alloy should of course be in harmony with the color of the object to be soldered, in order that the seams may be as inconspicuous as possible.

The fusibility of gold alloys varies as much as their color, and is lowered as the amount of gold in the alloy increases. Harder solders should therefore be used for objects of fine gold than for a poorer quality.

Gold solders are made from gold and silver, gold and copper, and still more frequently from a mixture of all three of these metals: in some cases zinc is added, to make the solder softer. But this must not be done if the soldered articles are to be colored, as the zinc alloy will turn black in coloring. For objects which are to be wholly or partially enameled, the solders made of gold and silver. or of gold, silver, and copper, are the only ones used, and these are called "enamel solders."

Pure Gold Solder

Hefore soldering apparatus had been devised by means of which platinum could be melted, pure gold was used for soldering articles made of this metal, such as are employed by chemists and in the manufacture of sulphuric acid. For this purpose, the gold is laid upon the seams in the form of fine rolled wire, or in thin strips, and melted with the oxy-hydro-gen blowpipe. But experience has shown that platinum articles soldered with gold are far less durable than those made by direct melting together of the pieces of platinum with the blowpipe, especially in the case of the vessel used in distilling the English sulphuric acid. Of late years this process has become universal in the manufacture of platinum ware, and the gold is only used for repairing small platinum articles, such as the small crucibles and dishes for chemical laboratories. It requires a fierce white heat to melt it properly, and it is even then rather hard, so that the process of soldering demands great skill on the part of the workman.

Hard Gold Solder

Gold 750/1000 fine (18 carat).................. 9

Silver ........................................ 2

Copper....................................... . 1

This is used for the finest gold articles.

Soft Gold Solder

Gold 750/1000 fine (18 carat).................... 12

Silver ........................................ 7

Copper ....................................... 3

This is likewise used for fine gold, but is much more fusible than the one first given.

Gold Solder for Articles 583 1000 fine ( 14 carat)

I.

Gold 583/1000 fine (14 carat).................... 3

Silver........................................ 2

Copper ....................................... 1

IT.

Gold 583/1000 fine (14 carat)................... 4

Silver ........................................ 1

Copper ....................................... 1

Gold Solder for Ordinary Gold Ware less than 583/1000 (14 carat) fine

T.

Fine gold..................................... 1

Silver ........................................ 2

Copper ....................................... 1

II.

Fine gold..................................... 1

Copper or silver............................. 1

Soft Gold Solder I

Fine gold.................................. 11.94

Silver ..................................... 54.74

Copper .................................... 28.17

Zinc....................................... 5.01

11.

Gold 583/1000 fine (14 carat).................. 10

Silver ........................................ 5

Zinc .......................................... 1

Enamel-Solder, Hard

Gold 750/1000 fine (18 carat).................. 37

Silver........................................ 9

Enamel-Solder, Soft

Gold 750/1000 fine (18 carat).................... 16

Silver ........................................ 3

Copper ....................................... 1

The degree of fusibility of the enamel must decide the question as to which one of these compositions to use. If it is very hard, the first solder is the proper one, as otherwise the seams would he-come so hot during the process of melting the enamel that the solder itself would melt. For ordinary gold ware soft enamels are generally used, and in this case the softer solder can be employed. It is easily melted with the common soldering pipe; the harder can also be melted in the same way, but the use of a special apparatus makes the process much easier and quicker.