[199] Allume di rôcca arso. Prof. Church tells me that this is probably sulphate of alumina, from alum shale.
[200] Boccia. Biringoccio in the fourth book of his ‘Pirotechnica,’ Venice, 1540, Chap. I., gives an illustrated description both of such an alembic and of how aquafortis for parting is distilled. See also the French edition of the same book translated by ‘Jaques Vincent.’ Rouen, 1627.
[201] Loto: the closing of the joints.
CHAPTER XXXVI. HOW TO MAKE ROYAL CEMENT.
Take the gold you wish to refine and beat it thin, cut it into little pieces of the size and the thickness of a golden scudo. Sometimes the scudi themselves are taken and a twenty-four carat cement refined direct from them; and this simple[202] cement has such virtue that it can draw all the alloy[203] out of the scudo itself without destroying the impression on the coin, but drawing from it only what was of base metal.
The cement is made in this wise: Take tartar and brick dust and make a paste of them; construct a round furnace[204], & into the joints of the furnace between one brick and another spread the paste; put your pieces of gold, or the scudi themselves, if you use them, into the paste, and cover them well up with more of it; then fire for twenty-four hours, at the end of which time they will be refined to twenty-four carats.[205]
Know, gentle reader, that this screed of mine is not writ for the purpose of teaching such as are refiners[206] by profession how to make aquafortis, my only care is to show how & to what end it may serve the art of goldsmithing; for it came about that having made certain golden figures half a cubit high for King Francis, when they were near the ending, during the softening in the fire, it happened they got a film of lead fumes across them, and had I not covered them over with this cement lotion they would have gone brittle as glass.[207] Then I gave them six hours moderate firing, and so in this way freed them from so evil a blemish.
THE END OF THE TREATISE ON GOLDSMITHING.
FOOTNOTES:
[202] Cellini may intend a stronger sense to the word ‘semplice.’