It is a matter of astonishment to me that glass painters do not use a ruby stain, which, with a little practice, can be managed quite as successfully as the yellow silver one. It is true that it would be impossible to fire the ruby and the silver stains together, and it would not be at all convenient to fire the ruby stain at the first firing of the painted glass. The method of staining ruby is as follows: grind up carefully some black oxide of copper, mix it with water (or with a small quantity of gum added), float it on the parts to be coloured, place it in a kiln and heat it. Black oxide of copper, when mixed with glass and melted in a glass-pot, makes the glass green; suboxide of copper, which contains less oxygen than the black oxide, when treated in the same way, makes it red. Now, if it can be reduced to the lower oxide of copper, while the black oxide of copper on the surface of the glass is heated, it will then colour the glass red. The best way of reducing the black oxide, is to connect the muffle with a gas-supply pipe, and allow coal gas to pass during the whole time that the heating process goes on. The action of the gas, which contains hydrogen and carbon, is to take away oxygen from the black oxide of copper, when it is at a high temperature; and, as soon as sufficient is taken away by the hydrogen to reduce the black oxide to the state of suboxide, it stains the glass red. It does not matter if the reducing action be continued longer, so that the oxide of copper be reduced to the metallic state; for at that temperature, the stain produced by the red oxide of copper is not removed by the continued action of hydrogen gas. The employment of this process would certainly enable artists who paint in the later styles of glass painting, to very much enrich their draperies, and to produce, more easily, effects which now can only be obtained by a complicated system of lead-work.