Silver Solder.
—This can be purchased at prices up to 3s. 6d. or so per ounce in sheet form, about 1⁄32 in. thick. Where the solder is melted down by the amateur, a good way to obtain the sheet form is to turn the globule of molten metal on to the bench and to place a flat iron on it; but the result will not be equal to a rolled ingot.
An old shop method of making silver-solder is to melt up old silver (using current silver coinage is an expensive method of obtaining the silver, and is said to be illegal) with some brass pins, not the iron ones so common now.
According to W. H. Jubb, two solders compulsory for silver articles that have to be sent to assay for hallmarking are: (1) 12 parts standard silver and 1 part brass; (2) 6 parts standard silver and 1 part brass. No. 1 has a low melting point, and is termed “quick,” and No. 2, which requires a higher temperature, is called “stark” (in some parts of the country, “fine”), but the use of this term here is misleading. No. 2 should be used at the first heating and No. 1 at the second. These should make ideal solders for beginner’s use, as the chances of burning the work, even thin brass, are almost nil.
(3) 2 parts brass, 1 part standard silver; (4) 5 parts brass, 2 parts standard silver. Whereas Nos. 1 and 2 are “silver solders,” Nos. 3 and 4 are termed “German silver solders,” as they are not so white and are used on German or nickel silver (an alloy of copper and nickel). Both Nos. 3 and 4 are good, have a comparatively low melting point, are much less expensive than Nos. 1 and 2, and, if plenty of wet borax is used, will “strike up” well. No. 3 is recommended.
“Standard silver” is about 95 per cent. pure silver. Old “sterling silver” is 92·5 per cent. pure silver.
In making any of the above solders the brass and silver should be melted together, and care should be taken to see that the metal is clean beforehand. Where large quantities of solder are made, the metals are scoured with emery cloth before they are put into the crucible.
Requisites for Silver-soldering.
—For light jobs in silver-soldering the special tools and materials required are as follow: Suitable gas jet or other flame, mouth blowpipe, scraper, jar containing a sulphuric acid “pickle,” piece of slate, camel-hair brush, pieces of lump borax, two grades of silver solder, charcoal block, iron binding wire.
The pickle is made by pouring 1 part of common sulphuric acid into 20 parts of water, and its function is to remove all dirt and borax from the metal. Silver-soldered articles should not be thrown into the pickle until they are nearly cold, as otherwise the joints may crack, but in the preparatory annealing (that is, softening) of plain metal, wire, rod or tubing, the article may be put into the pickle when hot—but take care of the splashes! Plunging hot copper or brass into cold water does not have the effect of hardening it. Before placing a job in the pickle, remove any iron binding, as this is immediately attacked by the acid.