(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
Driers, or Siccatives
Driers, or siccatives, are usually metallic salts that are combined with oils or resins and then mixed into the paint and/or medium and/or varnish to accelerate the drying time by speeding the rate of oxidation and polymerization. But it is important to remember that driers diminish the life of the paint or varnish. With good judgment and experience, however, they can be used safely. The following guidelines may prove helpful.
1. Use a drier only in glazes or in thinly painted pictures.
2. Never use more than 3 percent concentrate to media consisting primarily of a drying oil, and 6 percent to oil-resin media combinations.
3. Never apply a faster-drying paint film over a wet, slower-drying paint film.
4. Test a drier before use on something other than your final picture.
Cobalt drier, siccative de Courtrai (primarily lead linoleate), and siccative de Haarlem (primarily dammar resin) are among the more common driers. Cobalt and dammar are the least harmful because they work primarily while the paint is in a liquid state, their action becoming progressively less as the paint film hardens. This is not the case with lead driers, which can continue to act even after the paint film hardens. Siccative de Haarlem is safer than siccative de Courtrai because of its lower lead content and proportionately larger amount of dammar resin. Similar drying effects can be obtained by mixing small amounts of faster drying colors into slower-drying colors, for example, mixing cobalt, manganese, viridian, and lead-containing colors with slower-drying colors such as phthalo blue or lamp black.