Manufacture of Guignet Green on a large Scale.

Practical Magazine 13, 1876

(Chemistry applied to the Arts, Manufactures, &c. Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

This beautiful colour, which in its tint and brightness rivals Schweinfurt green, and has the great advantage over it of being free from poison, is, as is well known, a hydrated oxide of chromium, produced in a peculiar manner. It may be easily prepared in large quantities by melting together to a dull red heat a mixture of three parts of boracic acid and one of bichromate of potash on the hearth of a reverberatory furnace constructed for this purpose. The mass swells up, disengages oxygen in abundance, and ultimately changes into a beautiful green combination of borate of chromium and potash. Successive wash ings with boiling water separate it into hydrated oxide of chromium and soluble borate of soda. When the washing is over it is bruised fine, and a colour is obtained of the most beautiful tint, which covers well, resists the air and light, and is affected only by concentrated boiling acids. It may be easily prepared in small quantities in a porcelain crucible.

- Technologiste