Other organic materials such as leather, skin and textiles were treated similarly, by keeping them moist in tanks or sealed plastic containers. Bone and ivory was desalinated to prevent damage from salt crystallisation, as were glass, ceramic and stone. Iron, copper and copper alloy objects were kept moist in a sodium sesquicarbonate solution to prevent oxidisation and reaction with the chlorides that had penetrated the surface. Alloys of lead and pewter are inherently stable in the atmosphere and generally require no special treatment. Silver and gold were the only materials that required no special passive storage.