Novel paint solvent and paints thinned with such solvents are disclosed. In one disclosed embodiment the paint solvent is an aqueous solution containing a high concentration a strongly alkaline agent containing calcium ion as its main cation. Another solvent is disclosed which is a homogeneous blend of (a) an aqueous solution containing a high concentration a strongly alkaline agent having calcium as its main cation and (b) an an aqueous solution obtained by treating seawater with the strongly alkaline agent. The strongly alkaline agent contains at least 40% by weight calcium oxide and is a product obtained by calcining a calcium-containing natural substance such as shell, bone, limestone or mixture thereof.
A protective coating on a metal surface comprises a particulate material produced by a method including heating an animal skeletal material to a temperature of at least 1000.degree. C. for a time sufficient to convert at least part of the calcium carbonate in the skeletal material to calcium oxide and produce a calcined product; and then contacting at least part of the calcined product with water to produce the particulate material containing calcium hydrate.
