Oil drying agent

Desiccants (of siccus latin, dry) are substances that are oil-based paints and coatings may be added to speed up the drying process.

Chemical Reaction

The " drying process " of oil paint is chemically oxidation, polymerization and cross-linking with increasing the molar mass, in which the " drying " oils first decrease in volume, but then again shrink ( first wrinkle, then cracking ), eg linseed oil will Linoxin. The viscosity of the oil increases. It is at this viscosity increase of a cross-linking polymerization and not a loss of the solvent as a drying process. Driers act as catalysts in these processes.

Use in oil painting

Desiccants are in oil painting an important component of color to accelerate the drying process. The basis of the colorants drying oils are used. The actual oxidation process with and without desiccant is a continuous process that can extend over centuries.

Through the use of desiccants can be the time that oil paint takes to " brand dry" to be 5-12 days ( linseed oil, thin application, depending on pigments used ) to a reduce to two days. Excessive use is a premature aging process, which makes in strong Runzelbildungen and yellowing noticeable, in the following also in severe cracking. Siccatives are commonly used heavy metal oxides of Pb, Mn, Co, Zn, and the metal salts ( metal soaps = ) of the most unsaturated fatty acids such as oleic acid. Pigments with these heavy metals such as lead white have their own desiccants effect based on saponification with increase in viscosity.

In practice, mixtures of different metal soaps are widely used. Solutions of driers in oil - sometimes referred to as Sikkativextrakte - are often turbid after standing. Then allowed to settle for clarification in open vessels.

" A Mennigsikkativ is obtained when boiled linseed oil varnish with red lead and umber with constant stirring until a musähnliche mass is obtained, and this diluted with turpentine. The clear varnish is poured off after a few days of the sediment. For zinc white color is boiled linseed oil with 5% manganese dioxide powder, which is sewn into a sack of canvas, the one mounted in the boiler that it does not touch the ground. Continue boiling twice for 10 to 12 hours and then diluted with turpentine. The dark brown liquid obtained given larger quantities of oil and varnish the ability to dry quickly. Most commonly used borate of manganese, which you anreibt with little linseed oil and boil with about 300 to 400 parts of linseed oil once. Zinc white, mixed with 5 % borate of manganese, comes as Siccatif zumatique in the trade and makes boiled linseed oil paints dry faster when adding the same to them 2.5%. Solutions of shellac in ammonia or in borax solution be used as a desiccant. The use of desiccants is advised especially in earthy colors, ultramarine and zinc white, superfluous at paintings with white lead, red lead, chrome yellow, as these colorants were already doing -drying. "

Health Note

The heavy metal ions contained in most driers (cations of lead, manganese, cobalt, zinc, etc. ) are not toxicologically acceptable.