Black Glass.

Practical Magazine 19, 1876

(Chemistry applied to the Arts, Manufactures, &c. Miscellaneous)

The articles made at Venice of black glass are distinguished above all other productions of that sort by their deep black colour, and on this account meet with much favour. Dr. KAYSER, of Nürnberg, investigated the composition of a frit from a Venetian glass factory, and also some black glass wares made there. The following were the results: —

The glass frit had the ordinary appearance of a frit, and showed under the microscope isolated small pieces of black glass. In hot water 29.7 per cent. were soluble, consisting of alkalies and salts of magnesia. These were in combination with carbonic acid, chlorine, and sulphuric acid.

The frit, out of 100 parts, contained:
Silicic acid .......... 55.57 parts.
Clay .......... 2.08 "
Oxide of iron .......... 1.25 "
Protoxide of manganese .......... 1.80 "
Carbonate of lime .......... 8.88 "
Sulphate of magnesia .......... 3.95 "
Sulphate of soda .......... 3.55 "
Hydrochlorate of potass .......... .55 "
Hydrochlorate of soda .......... 10.66 "
Carbonate of soda .......... 11.85 "
[TOTAL] .......... 100.14 "

A rod of black glass, such as is used for the manufacture of glass pearls, out of 100 parts, contained: —
Silicic acid .......... 69.69 parts.
Clay .......... 1.94 "
Oxide of iron .......... 2.43 "
Protoxide of manganese .......... 11.39 "
Lime .......... 7.53 "
Magnesia .......... 1.26 "
Soda. .......... • 5.41 "
[TOTAL] ..........99.65

From the above analysis it was probable that the black colour of the glass is caused by the large proportion of manganese in it. To certify this conclusion, a mixture of sand, soda, and powdered manganese ore (to the extent of 15 per cent.) was melted in a Perrot's glass furnace. The glass substance obtained was deep black while in very thin layers, and dark violet when drawn out in very thin threads, as well as in thin splints. Hence, in point of colour, it was exactly like the Venetian black glass.

- Gewerbehalle, June, 1876.