92 - A Way to Make Hard Pastes in All the Calors
Have rock crystal, calcined and ground in a mortar, as was described distinctly in its place [chapter 76]. As an example use 10 lbs of this, and 6 lbs of Levantine polverino salt, extracted in a glass urinal, and very well purified, as was described in its place in the first book in the third chapter.
Dry this salt well and grind it over a porphyry stone. Pass it all through a sieve, and mix it in thoroughly with the above crystal. Then have 2 lbs of sulfur of Saturn made chemically,
as was described in its place [chapter 91]. Unify these three powders very well in a clean glazed earthen pan, and make it into a paste with clean common water. Use only a little water so the paste is hard.
Make small cakes of 3 oz, and make a hole in the middle of each. Dry them in the sun, then move them to a pottery furnace to calcine, in the upper part of the furnace, or other similar fire. Then break up these small cakes, and grind them over porphyry stone thoroughly, passing the material through a fine sieve. Then move this into crucibles in the furnace and leave the glass to clarify for 3 days. Cast it into water, and then reheat it, and leave it to clarify thoroughly for 15 days. At this point, all the imperfections and the bubbles
will be gone.
What remains is a most pure paste, like the natural gems, and furthermore this most pure type of glass will tint in any of the colours that you want. As an example use thrice cooked copper for an emerald colour, as was done in the ordinary glass; also use the copper for an aquamarine; use zaffer for topaz; and use zaffer and manganese for sapphire.
As with the ordinary glass, add the tincture once the glass has clarified and with the same diligence. You can make yellow with wine dregs and manganese adding them in parts, or even
a garnet colour with manganese and zaffer added in parts.
Make the glass as usual, and the effect will imitate all the gems in all the colours. This glass paste is most fine and will be quite hard, and have a shine, and polish of great wonderment. lt closely imitates the natural stones and is nearly the same in hardness, especially the emerald; with this method, it will be most beautiful and almost as hard as the natural stones.