If sulphur from the lye with which sal artificiosus is made, is strong enough to float an egg thrown into it, and is boiled until it no longer emits fumes, and melts when placed upon glowing coals, then, if such sulphur is thrown into the melted silver, it parts the gold from it.
To two librae and a half of such stibium are added two librae of argol and one libra of glass-galls, and they are melted in an earthen crucible, where a lump likewise settles at the bottom; this lump is melted in the cupel. Finally, the stibium with a little lead added, is melted in the cupel, in which, after all the rest has been consumed by the fire, the silver alone remains. If the stibium is not first melted in an earthen crucible with argol and glass-galls, before it is melted in the cupel, part of the silver is consumed, and is absorbed by the ash and powder of which the cupel is made.
The crucible in which the gold and silver alloy are melted with stibium, and also the cupel, are placed in a furnace, which is usually of the kind in which the air is drawn in through holes; or else they are placed in a goldsmith's forge.
Just as aqua valens poured over silver, from which the sulphur has parted the gold, shows us whether all has been separated or whether particles of gold remain in the silver; so do certain ingredients, if placed in the pot or crucible "alternately" with the gold, from which the silver has been parted by stibium, and heated, show us whether all have been separated or not.
We use cements[18] when, without stibium, we part silver or copper or both so ingeniously and admirably from gold. There are various cements. Some consist of half a libra of brick dust, a quarter of a libra of salt, an uncia of saltpetre, half an uncia of sal-ammoniac, and half an uncia of rock salt. The bricks or tiles from which the dust is made must be composed of fatty clays, free from sand, grit, and small stones, and must be moderately burnt and very old.
Another cement is made of a bes of brick dust, a third of rock salt, an uncia of saltpetre, and half an uncia of refined salt. Another cement is made of a bes of brick dust, a quarter of refined salt, one and a half unciae of saltpetre, an uncia of sal-ammoniac, and half an uncia of rock salt. Another has one libra of brick dust, and half a libra of rock salt, to which some add a sixth of a libra and a sicilicus of vitriol. Another is made of half a libra of brick dust, a third of a libra of rock salt, an uncia and a half of vitriol, and one uncia of saltpetre. Another consists of a bes of brick dust, a third of refined salt, a sixth of white vitriol[19], half an uncia of verdigris, and likewise half an uncia of saltpetre. Another is made of one and a third librae of brick dust, a bes of rock salt, a sixth of a libra and half an uncia of sal-ammoniac, a sixth and half an uncia of vitriol, and a sixth of saltpetre. Another contains a libra of brick dust, a third of refined salt, and one and a half unciae of vitriol.
Those ingredients above are peculiar to each cement, but what follows is common to all. Each of the ingredients is first separately crushed to powder; the bricks are placed on a hard rock or marble, and crushed with an iron implement; the other things are crushed in a mortar with a pestle; each is separately passed through a sieve. Then they are all mixed together, and are moistened with vinegar in which a little sal-ammoniac has been dissolved, if the cement does not contain any. But some workers, however, prefer to moisten the gold granules or gold-leaf instead.