73 - A Method to Tint Rock Crystal the Colour of a Viper Without It Melting.
Take pieces of rock crystal of various sizes that are crystal clear and without sediment; like limpid pools. Then have some of the crucibles that goldsmiths use, that resist the fire. Now,
take for example, 2 ounces of pulverized crude antimony, 2 ounces of that good yellow orpiment, pulverized, and 1 ounce of sal ammoniac. Thoroughly pulverize all these, mix them, and place in the bottom of a crucible.
Lay the pieces of rock crystal upon the powder, and then cover the crucible with another crucible. That is to say, mouth to mouth, and cement them together securely. When this is dry, put it in among the coals, which you should kindle little by little. As they begin to catch fire, leave the crucibles to inflame. They will feel the heat of the coals and begin to smoke quite a bit.
Perform this operation under a large chimney, and when the fumes begin to assault you [ skull].
This smoke is most injurious, and could be deadly; therefore, you should see that no one inhales it in any way, because it would do very great damage. When all fumes pass, you should nevertheless leave the crucibles in a low fire, until it goes out completely.
When the crucibles become cool, take and moisten the seal, and remove the pieces of crystal. You will find those on top tinted beautifully in areas, the colours of golden yellow, ruby red, and balas. Those on the bottom, upon the powder and its residue, will be tinted the serpentine colour of a viper.
Furthermore, you may work these pieces of crystal at the wheel, like gems. They take a beautiful polish and Iuster, and have an attractive luminance in the colours of topaz, ruby, and balas. If you back them with metal foil that matches their colour, they will look quite attractive when set in gold. You can tint a large quantity of these crystals at very little expense or trouble, and quite a few always come out, some of them sightly and beautiful.