Although the use of tannin for the treatment of water to protect steam boilers from corrosion had been suggested for more than a half century, the first use of antirust protection outside this field was in 1930. A renewed interest in this process occurred when nonarchaelogical objects buried in a medium containing substances of a tannic nature were found to be remarkably well preserved. There are two principal types of tannins, hydrolyzable and con densed. The potential oxidation of the phenolic groups of both types makes them strong antioxidants. Their phenol and carboxyl groups form complexes with metals. Tannification of iron does not spoil other materials in the presence of the iron, such as wood. Tannin solutions can be used to conserve objects with a light rust. The rust is converted by the process and the subsequent drying to strong and resistant layers, connected with the metal base. These form a suitable pretreatment for the application of varnish or coatingsTannin may also be used on objects with thick layers of rust, which are thus converted to a powdery material easily removable mechanically, while a tannate film of suitable protective qualities forms directly on the metal. Describes application with a brush of tannin solutions, as well as the ripening process of the tannate layer. For objects lightly rusted a solution of 200 g tannin in 1 liter of distilled water plus 150 milliliters of alcohol is suggested. To treat objects more heavily rusted it is necessary to add phosphoric acid to the first coat.