We understand additives to mean any substances that are added to increase the stability or the ease of use. Examples include siccatives, preservatives, anti-oxidants, fluidifying agents and thickeners.
A siccative is a solution of metal compounds that is used to speed up the chemical drying process of oil paints. Use it very sparingly and minimise it use.
The drying of oil paints can occur on the surface and deep in the paint itself. Depending on the metal compounds that make up a siccative, either the depth drying or the surface drying will be stimulated.
Types of and differences between siccatives
Siccative Courtrai consists exclusively of a solution of metal compounds, whilst Siccative Harlem also includes a certain percentage of oil. Siccative Harlem is therefore fatter and can be regarded as a quick-drying medium. The choice of siccative depends on the composition of a painting. As layered painting always requires the "fat-over-lean" technique to be followed in connection with a good adherence between the paint layers, it is not advisable to use the fatter Siccative Harlem in the lower layers. The incorrect use of siccatives can lead to problems. Apart from the drying process, the addition of a siccative also speeds up a painting's ageing process. To avoid problems, never add more than 2% Siccative Courtrai to the paints and never more than 5% of Siccative Harlem. In general, the use of siccatives must be kept to a minimum.