The classification followed in this section is the usual one of chemical constitution.

Carbons

The prominent paint pigments of the carbon group are graphite and lamp-black, or soot. They depend for their coloring principle upon the carbon contained in them, and, if well made, have no chemical action upon the liquid with which they are used. But, with the possible exception of wood charcoal, it is not recommended to use carbon paint as primers on steel.

Graphite exists in two forms—amorphous and crystalline, or fibrous. The crystalline form, 80-95 per cent. carbon, includes kinds called    globular,   granular,   foliated,   scaly,