Carbon is the coloring agent in almost all black pigments. These pigments are of organic origin, being products of either animal or vegetable matter. In a general way, these pigments may be divided into two classes depending upon their manner of production - charcoal blacks and soot blacks.

Charcoal blacks include ivory, bone or drop black, mineral, cork and vine blacks. The soot blacks include lamp black, vegetable blacks and carbon or gas black.

Ivory and Bone Blacks are made by calcining bones in some form of retort or closed vessel, which can be subjected to great heat. The quality of the product depending upon the nature of the bones used, and the temperature at which the calcining process is carried on, together with subsequent treatment. The best ivory black was originally made from calcined ivory chips. It is a dense, brilliant black, quite permanent, but not so powerful as some of the vegetable blacks. It consists of bone earth stained with a certain percentage of carbon formed in the calcining process. When used alone, it is superior to most other blacks, but when combined with other pigments of organic origin, it is apt to exert a bleaching action on such substances, being an active decolorizer because of the phosphate of lime it contains. Its absorbent powers are also very great, rapidly taking up moisture.

Charcoal Blacks are produced by calcining in closed vessels, wood and woody fibre; such materials as cocoa nut shells, the stones from various fruits, particles of cork and the stems of grape vines. Frankfort black is made from wine lees. Charcoal blacks have the same decolorizing property as bone blacks, but in lesser degree.

Mineral black is made from certain bituminous shales or coals by calcination.

Lamp black is produced by burning rosin, rosin oil, fats, and fatty oils, coal tar oils, and petroleum residues with a restricted supply of air, whereby much of the carbon they contain is deposited in the form of soot. The best and finest grades of black are those which are condensed furthest from the condensing chambers. They contain from 80 to 90 per cent. of carbon, which substance regulates their strength. The strongest black is that made by condensing the products of combustion of natural gas; known as gas or carbon black. It has remarkable strength and must be thoroughly and finely ground to give good results. It is used to strengthen weaker blacks and in the manufacture of black paints.

We must not overlook graphite or plumbago, a natural form of carbon before mentioned. It is not affected by most chemicals and gases, takes a large amount of oil and makes a very superior paint for all metallic surfaces.

Ivory black is best for decorative effects, where pure color is to be used. Carbon black is indicated for tinting when brown gray colors are desired. Lamp black, when blue grays are required. Vegetable blacks do not make good paint for metallic surfaces.

The general rule may be laid down that metallic or mineral pigments are best on metal; mineral pigments, containing silica on stone work; and carbonaceous or vegetable colors on wood work. For this reason, white lead containing carbon black or lamp black seems to produce a more lasting coat on wood, than white lead alone.