The chemical hardening of unsaturated liquid binders by means of the reaction with atmospheric oxygen is described as “drying”. Metal-organic compounds (metal soaps or complex) are used in relatively small concentrations to control drying processes. Such additives are described as driers. From the chemical standpoint, driers are molecular (homophase) catalysts for free radical oxidative polymerization, which is a chain process developing in the presence of the atmosphere oxygen.