The white enamel for hollow ware is made of powdered flints, ground with calcined borax, fine clay and a little feldspar. This mixture is made into a paste with water, and brushed over the pots, after they have been thoroughly scoured with dilute sulphuric acid and rinsed clean with water. While still moist, they are dusted over with a glaze composed of pulverized feldspar, carbonate of sodium (dry), calcined borax and a little oxide of tin. Thus prepared, the pots are gradually dried, and then the glaze is fired or fused under a muffle at a bright red heat.
Some oxide of lead is occasionally added to the above mixture, but though it increases the fusibility of the glaze, it impairs its value, since it will not resist the action of acids in cooking.
If any article of tin be subjected to rapid scouring with the use of potash lye and some hard substance, a very satisfactory lustre can be obtained.
A lustrous black on brass is secured by the dissolution of carbonate of copper, which has been freshly precipitated while yet moist in strong liquid ammonia, enough of copper salt being used so that there will be a small undissolved residue. This carbonate of copper is made by mixing when hot a solution of equal portions of soda and cupric sulphate, then filtering same and washing off the precipitation. This solution of copper salt in ammonia is to be diluted with 1/4 its volume of water, to which the addition is made of 31 to 46 grains of graphite and the mass heated to 95 degrees or 104 degrees Fahrenheit. Clean the brass and put it in this pickle for a brief time (a minute or so) until it shows a full black shade, then rinse same in water, followed by an immersion in hot water, and dry it in sawdust. As the solution does not keep, no more should be made at a time than is necessary for immediate use.
To make a hole in hard steel use a compound consisting of 1/2 teaspoonful powdered salt, 1 gill vinegar, 20 drops nitric acid, 1 ounce sulphate of copper and 1/4 ounce alum.
If you desire to make platinum adhere to gold, a small quantity of 18-karat gold should be sweated into the surface of the platinum at almost a white heat in order that the gold may soak into the face of the platinum. The face thus secured is one to which ordinary solder will firmly adhere.
Thirty-three parts of copper and 25 of zinc are alloyed, the copper being first put into the crucible, which is loosely covered. As soon as the copper is melted, zinc, purified by sulphur, is added. The alloy is then cast into molding sand in the shape of bars.
Malleable Britannia Metal is composed of:
1 part Bismuth, 48 parts Zinc,
3 parts Copper, 48 parts Tin,