Aventurine Glass.

Scientific American 44, 24.7.1847

This costly and beautiful sort of glass, used for ornamentin objects of art and vertu, could not be hitherto made but at Venice. Only so much was known, that very minute crystals of metallic copper of great lustre, which mixed throughout the mass of dark reddish-yellow glass, imparted to this substance that lustrous and incandescent appearance for which it was so much prized. Messrs. Fremy and Calendau have lately laid before the French Institute their process for making this valuable substance. It consists of mixing powdered glass with hammershlag (black oxide of iron, or scales from the forge) and oxide of copper, and keeping the whole for a considerable time in a state of fusion. By these means the copper crystallizes in the glowing mass of glass in the shape of small octahedra, which being dispersed through the mass, imparts to it a beautiful scintillating appearance. Still, the original Venetian samples, and those made by Messrs. Fremy and Calendau, were not of equal quality - the mass of glass, wherein the cyrstals are emedded being, in the former case, clear and pellucid; in the latter, rather soiled, and barely transparent. The crystals in the Venetian are large and very regular; in the French small, irregular, and fibrous. The principle, however, is discovered; and it will only require, as with every thing else, time and experience to equal the Venetian patteras.