Sapphire. Paste 4608, oxide of cobalt 68, fused for 30 hours.
Amethyst. Paste 4608, oxide of manganese 36, oxide of cobalt 24, purple of Cassius 1.
Beryl. Paste 3456, glass of antimony 24, oxide of cobalt 11/2.
Styrian garnet, or ancient carbuncle. Paste 512, glass of antimony 256, Cassius purple 2, oxide of manganese 2.
The following recipes are given by M. Lancon:
Paste. Litharge 100, white sand 75, potash 10.
Emerald. Paste 9216, acetate of copper 72, peroxide of iron 1.5.
Amethyst. Paste 9216, oxide of manganese from 15 to 24, oxide of cobalt 1.
The ancient coloured glass has been much admired. The art was carried to a very great extent. Even in Pliny's time, the highest price was set upon glass entirely free from colour. He, as well as others, mentions that hyacinths and sapphires were imitated very exactly.
The emperor Adrian received as a present from an Egyptian priest, several glass cups richly ornamented with various coloured glass. Seneca speaks of the knowledge of Democritus in this art. Porta, Neri, and others, in modern times, have treated the subject in a more enlarged manner. Coloured glass was used for ornament; but Pollio relates, that Gallenius punished an impostor for selling to his wife a piece of glass for a jewel. In the Museum Victorium at Rome, are several ancient artificial gems, such as the chrysolite and emerald. What materials the ancients used for colouring glass is not known. Gmelin, however, observes, that it is probable they made use of iron, by which, he adds, not only all the shades of red, violet and yellow, but even a blue colour might be communicated. Cassius discovered the powder which bears his name. He was a physician, and resided at Lubec.[22] This powder was employed by the German artists. While noticing this subject, it may be proper to state, that Libavius (Alchemy, 1606,) gives a process for making ruby glass. Neri, (ars vitraria by Kunkel,) was acquainted with the gold-purple and its use. Glauber (Furnus Philosophicus, 1648) mentions the use, and gives the preparation of the powder. Kunkel made artificial rubies in great abundance, and a cup of ruby glass for the elector of Cologne. In 1679, he was inspector of the glass houses at Potsdam; and, in perfecting the art, he expended 1600 ducats, which the elector of Brandenburgh gave him for the purpose.