Techniques of Impressionism - Materials

Concerned about the permanence of their paintings and having individual requirements and preferences regarding colours as well as paint consistency, the Impressionist artists chose to avoid mass produced paints. They instead relied on personal recommendation and service and preferred colours to be grounded by hand. Some artists such as Cezanne, van Gogh and Renoir opted to pay for materials made by independent colourmen. Hand grinders used a cone shaped stone grinding the pigment on a hard non-porous, porphyry stone slab. After the pigment particles reached the desired size, the oil binder was added and the two were ground together. Mechanization and mass production gave colours a homogeneity of consistency that was unknown in hand grinding. Some artists opted for the mass produced colours, as they believed 'however conscientious a man may be, he cannot rival a precision tool.' Others found the new homogeneity a disadvantage because that meant in order to produce variations in opacity and transparency with the colors, one needed to add harmful thinning agents. If colours were prepared from the outset with their characteristically varied viscosity, harmful adulteration could be avoided. The newly introduced collapsible tin tubes extended the shelf life of oil paints, but additives were needed to prevent some colors from separating on standing. Therefore the choice of oil binders became crucial and thus artists sought new methods aimed at exploiting the new paint characteristics.

In the 1830's, an English colourman, George Blackman was recorded as introducing additives to give a stiffer paint consistency, including spermaceti or sperm whale oil. Max Doerner noted that sperm oil has been used now and then in place of beeswax in oil-colours. Other non-drying fats or oils like paraffin wax and castor oil were harmful to the paint layer. Stabilizers or thickeners made it possible to increase the volume of oil in the mixture without reducing its viscosity. The greater the quantity of additives, the more the manufacturer could skimp on the actual pigment, thus reducing the intensity of the color. Extenders were also sometimes added to the pigments. These inactive colorless agents were designed to extend the pigment and thus were used to economize on the quantity of the pigment required to achieve the desired paint consistency. Extenders are normally transparent and can dilute or diffuse colored pigments and improves a paint's wearing quality. Barium sulphate was commonly used as an extender.