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 we share with you articles from the unpublished book of Professor Theo de Beer “Everything about art materials”.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.
Sap green was first used in 1704, and is in both light and dark. Sap green, or bladder green, is made from the sap that is squeezed from the berries of the buckthorn ‘rhamus catharticus’. Chalk is then added. The dye is also called bladder green because it used to be stored in pig bladders to guard against dehydration. Nowadays, the colour is composed of synthetic pigments, which have roughly the same properties and can be lightfast.
The toxic sap green had high colour strength and was not lightfast. The transparent colour was also made from a mixture of Stil de grain yellow with Prussian blue pigment, which is not lightfast either. At the end of the 19th century, Stil de grain yellow was no longer available and Mr Hooker replaced it by the pigment gamboge (gummi-gutta). The paint colour can now be composed of lightfast transparent pigments, making this paint extremely suitable for practising the glazing technique. The layer of oil paint will start to wrinkle if you suddenly apply it in thick layers. The transparent paint is very popular as watercolour paint. See also Hooker’s green.