Siccatifs

Siccatifs are substances that promote drying, particularly in oils and paints. They are essentially drying agents that accelerate the oxidative polymerization process of unsaturated oils, transforming them from a liquid to a solid state. This process, known as autoxidation, is a chemical reaction where the oil reacts with atmospheric oxygen, leading to cross-linking of the fatty acid chains and the formation of a hard film.

The most common siccatifs are metallic salts, typically cobalt, manganese, lead, or zirconium salts of organic acids like linoleates or naphthenates. Cobalt and manganese are considered active driers, promoting surface drying. Lead, historically significant, promotes through-drying, ensuring the entire film hardens. Zirconium is often used as a through-drier and can be employed to replace lead due to health concerns.

Siccatifs are added in small quantities to oil-based paints, varnishes, and printing inks. Their function is crucial for the practical application and performance of these materials, allowing them to dry within a reasonable timeframe and form a durable, protective layer. Without siccatifs, many oil-based coatings would remain tacky for extended periods, rendering them unusable. The choice and concentration of siccatif depend on the specific oil used, desired drying speed, and the intended application of the coating.