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 dilution of metal compounds and helps to speed up the chemical drying process of the oil. Oil generally dries through drying on the surface and within the oil. Depending on the type of metal compounds used in the siccative, either the surface drying or drying within the oil will be promoted. The light siccative, Siccative Courtrai, speeds primarily the drying within the oil. The darker Siccative Harlem on the other hand accelerates the surface drying.