In the section “Prof. Theo de Beer about ….” we share with you articles from the unpublished book of Professor Theo de Beer “Everything about art materials”. Prof. Theo de Beer managed the Old Holland company from 1982 till 2000 and made a huge contribution to its development.
In 1859, the Frenchman Salvetat tried out a new method of preparation to make cobalt violet light. He wanted to replace the extremely toxic arsenic, which had been used for the production of cobalt violet light. But he obtained a different colour, which had a rougher structure and was much darker. The dark cobalt violet was composed by heating cobalt aluminate together with sodium phosphate, which was less toxic. Cobalt phosphate is PV 14.
Toxic cobalt violet dark is lightfast. The pigment, which has low colour strength, is not acid-resistant. Due to its poor alkali fastness, the pigment is also unsuitable for application on alkaline surfaces. The non-opaque pigment activates the drying of the oil, and provides a brittle layer of oil paint. In the violet colour range, there is little choice as regards the various nuances. It is almost impossible to make cobalt violet dark by mixing other colours. When used as a watercolour, the pigment particles remain visible on the paper. This type of paint often becomes hard in the tube or in the pan. Cobalt violet dark is unsuitable for making acrylate paint, because the pigment and the acrylate medium do not tolerate each other.