The Encyclopedia Americana (1920)/Blacks

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1341125The Encyclopedia Americana — Blacks

BLACKS. Black pigments are of two types: charcoal blacks or fixed blacks, and soot blacks. The charcoal blacks include those made by the carbonization of bones and ivory, as well as those made from charcoal of wood and animal refuse. The soot blacks include carbon black or gas black, and lamp black.

Charcoal black is made by heating wood in closed retorts till it is charred through and through, and grinding the residue, after which it is thoroughly washed. The finest grade of charcoal black is that made by carbonizing cork. It is fine, smooth and of considerable body. A highly esteemed grade is Frankfort black, also known as drop black and vine black. It is made by carbonizing twigs of grapevines, to which are added hop vines, peach and plum stones, and sometimes chips and shavings of bone. Animal black is the name given to the pigment produced by charring the offal of slaughter-houses. Cheap charcoal blacks are of poor covering power, but are excellent as preservatives, and useful especially in making the gray or “lead-colored” priming coat so commonly applied to new work by painters.

Bone black is prepared by grinding the carbonaceous matter resulting from the charring of bones in iron retorts. It contains about 15 per cent carbon; 78 per cent calcium phosphate; and 7 per cent calcium carbonate, alumina, silica and iron combined. It has a specific gravity of 2.7. The grinding does not produce a uniformly smooth powder, there being always more or less grit of hard charred bone. Ivory black is made sometimes of ivory waste but more commonly of selected bone. It is a favorite with painters, having a “tooth” which is lacking in the soot blacks. It is, however, slow to dry, and a drier is usually added. Its lack of covering power is helped out by the addition of some rich velvety black, generally lamp black. The highest grade of plate ink used by printers is made from the choicest bone black with the addition of vine black and a little Prussian blue. To make the ordinary paste in which form paints are usually marketed, bone black requires the addition of 50 per cent of its weight in oil. Large quantities of bone black are used by the sugar refineries to decolorize raw sugar in solution, no other substance having been discovered of equal or even approximate efficiency. After this use the bone black goes generally to the fertilizer manufacturers, but a part comes into the paint industry.

Carbon black, a very pure form of carbon, is made by the combustion of gas in a scanty supply of air. The flames are thrown against metal or slate slabs or upon revolving cylinders. The accumulating black is scraped off and ground. It has a granular texture and requires a great deal of grinding to make a smooth pigment. Carbon black has great staining power and requires 82 per cent of its weight in oil to produce the paste form in which it is marketed — as "ground in oil." In the dry form it was formerly packed in barrels, but was found to absorb moisture. This tendency has been overcome by packing it in paper sacks. The best grades of carbon black are used in making black varnishes and printers' inks. With white, carbon black gives brownish-gray hues.

Lamp black is a nearly pure carbon made by the combustion of oils in an atmosphere lacking in oxygen. The larger part of the commercial supply is made from the dead oils distilled from coal tar and from wood tar, petroleum, rosin, etc. The choice grades are made from seed oils. Any material which in a plentiful supply of oxygen gives a highly luminous flame will produce lamp black when the air supply is cut down. The oils are ignited in a limited supply of air so that the combustion is imperfect and intensely smoky. The smoke is passed through a long series of chambers, and against and around many upright partitions on which the soot or lamp black is deposited. In Germany lamp black is made by passing the smoke from resinous wood through hanging woolen blankets. The soot is shaken from the blankets at intervals. Ordinary lamp black will weigh from 100 to 120 pounds to the (flour) barrel; the finest grade will weigh but 30 pounds to the barrel. It is required that lamp black test not more than 0.2 of 1 per cent of ash. To make the buttery paste in which the tinned lamp black is sold requires 75 to 76 pounds of oil to 24 or 25 pounds of lamp black. As a pigment lamp black is noted for its remarkable covering power. The cheaper grades are made into common printing ink; the finer grades cannot be used for this purpose as they require more than the limit of 65 per cent oil, the utmost that can be permitted in printing ink.

According to the United States census of manufactures for 1914 there were in operation 27 establishments devoted exclusively to the manufacture of bone black, carbon black and lamp black. These establishments employed 437 persons, of whom 339 were wage earners receiving annually $230,821 in wages. The capital invested was $4,995,400, and the value of the year's output was $1,463,569, of which $777,329 was the value added by manufacture. In addition, there were 19 other establishments in which some of these products were made. The total production of blacks by all makers in 1914 was valued at $2,949,797; comprising carbon black, $900,630; lamp black, $517,167; and bone black, $1,532,000. Among the States, West Virginia ranked first in production of blacks, turning out 54.5 per cent of the entire product of the country. Pennsylvania ranked second. Both of these States make their product from natural gas.