Kuivumisöljyjen

Kuivumisöljyjen, commonly translated as drying oils, are a class of natural oils that undergo a chemical transformation upon exposure to air, hardening into a solid film. This property makes them valuable in various applications, most notably as binders in paints, varnishes, and inks. The drying process is a form of oxidation, where the unsaturated fatty acids within the oil react with atmospheric oxygen. This reaction is typically catalyzed by metal salts, known as driers, which accelerate the polymerization and cross-linking of the oil molecules.

The degree of drying is determined by the iodine value of the oil, which indicates the amount of unsaturation present. Oils with high iodine values, such as linseed oil, tung oil, and poppy seed oil, are considered highly drying. These oils have a significant proportion of polyunsaturated fatty acids, particularly linoleic and linolenic acids, which readily form peroxides and then cross-link to create a durable, protective film. Less drying oils, like olive oil or almond oil, have fewer double bonds and therefore do not harden effectively when exposed to air.

Historically, drying oils were the primary binder in oil paints, providing both color adhesion and a protective layer. While modern synthetic binders have largely replaced them in many industrial applications, drying oils remain important for artists seeking traditional paint qualities and for specialized finishes where their natural properties are desired. The hardening process can take days or even weeks, depending on the oil, the presence of driers, and environmental conditions like temperature and humidity.