To test the damage to metals by free fatty acids of various types, aluminum, iron, copper, silver, tin, and zinc rings were first weighed, then immersed in oleic acid, stearic acid, or marine (oil) fatty acid, cleaned and weighed again. Aluminum, iron, and silver showed little or no damage. However, copper, zinc, and tin were strongly affected. Copper was especially strongly affected by oleic and stearic acids. This qualitative test was followed by a quantitative test using the same materials. To test damage to leather caused by compounds of fatty acids and metals, vegetable-tanned leather was impregnated with iron, copper, tin, and zinc salts of stearic acid, oleic acid, and marine (oil) fatty acid, whose preparation is described. Since no solvent could be found for the previously prepared aluminum and silver salts, they could not be used. Tear strength diminished with the amount of infiltration, length of storage, and increase in storage temperature. -- AATA