The chemical process that occurs during the preparation of varnish

The chemical process that occurs when oil is boiled with metal compounds, i.e. during the preparation of hot varnish

Under the influence of temperature, oil with added metals (lead, cobalt, manganese) partially saponifies. In doing so, they are formed:

• free fatty acids (formate, acetic, oleic and others);
• part of the liberated glycerol turns into accreoline (a suffocating gas formed when fats are cooked).

Free fatty acids enter into a compound with metals and form so-called linoleates (soaps).
During cooking, only part of the oil is broken down, accompanied by the above chemical process.
Much of the oil still consists of glycerides after cooking.
Linoleates can be obtained as separate preparations, which are used to prepare varnishes when the oil is heated weakly (100 ÷ 150°C) or completely cold.
A light varnish is then obtained.
Resinates, or resinates, are obtained by fusing rosin with metals. Resinous salts of fatty acids (soaps) are formed.
Fused linoleates and resinates have the appearance of colored, hard or soft, pieces, as well as a thick liquid or powder.
Siccatives are deposited as white or colored powder. Both are soluble in oil or volatile solvents.
Nowadays, cobalt linoleate and cobalt resinate are most commonly used, as they not only speed up the drying of oil, but also bleach it.