The Chemistry of Paints and Painting is a free textbook on chemical aspects of painting. See the editorial for more information....

Venetian Red

Synonyms: Venetian Red, Rouge, Crocus, Colcothar, Caput Mortuum Vitrioli, Venetianischrot

Originally Venetian red consisted of a native ferric oxide or red hematite, less purplish in its tints and washes than Indian red. But of recent years the name appears to have been transferred to a particular quality of artificial ferric oxide, made by calcining green vitriol. When this salt is heated in a crucible the upper portion of the product, which has been less strongly heated than the lower, is of a brighter red than the remainder, and after washing and grinding is sold as Venetian red. If moistened with a solution of nitre, again heated, and then ground and washed, the red tint of the product becomes somewhat brighter.

The hue of Venetian red is less brownish than that of light red, and not at all purplish like that of Indian red.

Venetian red, whether artificial or natural, is a permanent pigment which may be mixed with other permanent pigments without fear of injuring them; but it must be perfectly free from soluble salts and from any trace of sulphates. The presence of the latter may be detected by the test described under 'Light Red' and 'Indian Red.' But few commercial samples will stand this test, however, and we consequently find that many samples of Venetian red, owing to the presence therein of sulphates, exert an injurious action upon some of the organic pigments used as water-colours - notably, upon indigo.

A very fine native red ochre comes from Tuscany and from Krasso in the Banat, Hungary. It is represented by the formula 2Fe2O3, H2O, and goes under the minera-logical name of turgite. Its hue is that of a fine Venetian red: it is probable that the fine native Indian reds and red ochres sometimes consist of or contain this hydrated ferric oxide, and are not really anhydrous.


Last Update: 2011-01-23