Lampblack without question is the black pigment most commonly used of all the line of oil colors, and no assortment of these is complete without it. Of course, very large quantities of lamp black are sold in the dry powder, packed in round papers or square paper boxes from one-fourth pound to one pound. The brands most popular are known as Germantown, with a special trade-mark, such as "Eagle" or "Bear," etc., for the best grade, also "Old Standard," or "Ordinary," "Star," "Coach Painters'," "Sign Writers'," or other fancy names. These do not interest the color grinder, as he buys the material in bulk, packed in casks, barrels or sacks. While formerly Germantown lamp black in bulk was a favorite with color grinders, the keen competition of the last two decades forced them to look for lamp black of greater staining power and induced lamp black manufacturers to cater to this want. To be up with the procession every color grinder must have for his best brand at least a lamp black that will, when ground in oil to the usual paste consistency, show twice, or nearly twice, the tinting strength of the better grade of Germantown lamp black, and when separated from the oil in which it is ground in a chemical analysis it must not show more than two-tenths of 1 per cent of mineral ash if it is to pass the specifications issued by government service departments. Nor must such black show any unburnt oil or tarry matter, as their presence retards the drying of the pigment when ground in oil. To ascertain the presence of such undesirable matter a very simple test is sufficient. A small hillock of the dry black is placed on a piece of perfectly white blotting paper and the black saturated with sulphuric ether. The ether will be absorbed by the blotter, forming a ring or halo on the outside of the black, and if any em-pyreumatic matter is present in the black the ring will show yellowish or brownish discoloration, whereas if it remains clear the black is free from such deleterious matter. The next thing is to test the black for absence of grit and also to try it out for tinting power by assaying it in the usual manner with zinc white, comparing it with an adopted standard.
To be perfectly safe when selecting grinders' lamp black on large orders or contracts the color grinder should secure enough of each black offered to make a practical mixing and grinding, so as to ascertain the exact percentage of oil required for each brand of black under consideration, and by making his tests for fineness and strength with the finished products in comparison with one another he will have no trouble to decide which of the blacks it is most advantageous for him to use. A lamp black of this description has a specific gravity of 1.80 to 1.84 and will require seventy-five to seventy-six pounds of oil for every twenty-four to twenty-five pounds of the dry black to form a buttery paste that will break up nicely when being thinned for use. To grind it in oil iron or steel mills are preferable to stone mills, because increasing the output, while buhr stone mills should not be used at all for grinding lamp black in oil. Lamp black of the class here described is soft and esopus stone mills will turn out a smooth paste. All of the foregoing refers to lamp black made from residuums of oils, fats, greases, petroleum and tar oils. When black is offered that is made from vegetable matter it can be readily identified by its harsher, coarser texture and its heavier gravity. A grinders' lamp black of the above description when packed in flour barrels will weigh no more than thirty pounds net. while a sugar barrel will hold about forty-five pounds - a sugar barrel will hold about sixty pounds of a fairly good grade of Germantown lamp black. Commercial lamp black as a rule is very heavy in gravity and a flour barrel will hold as much as 100 to 120 pounds, but it is scarcely ever used in color grinding, excepting, perhaps, in cheap black paints where it is necessary to economize in the use of oil.
As we have remarked when speaking of carbon black it is very difficult to mix oil lamp black with water, and when lamp black is wanted ground in water carbon black is, as a rule, substituted for it, although by the exercise of much patience lamp black can be mixed and ground in water. Place the required quantity of dry black in a mixing pot of convenient size, then put water on the powder, little at a time, to saturate and let stand over night. Making the water alkaline with carbonate of soda will also aid in obtaining a mixture, one ounce of soda to twenty-five pounds (three gallons) water.
Lamp black in japan is not much called for at present, still it is listed by coach color manufacturers and is being used by sign painters for quick work and for similar reasons by some coach and carriage painters. For this purpose it is best ground in three parts coach japan and one part turpentine, rather stiff in consistency, on a twenty-inch or twenty-four inch water-cooled mill (iron or steel mill preferable) and then to every forty-five pounds of the product should be added five pounds of good rubbing varnish, running this mixing loosely through the mill. A good average formula would be as follows: - Twelve pounds grinders' lampblack, twenty-seven pounds coach japan, nine pounds gum spirits of turpentine, equal to forty-eight pounds. Result, about forty-five pounds paste. Add five pounds rubbing varnish. Final result, fifty pounds lamp black in japan, with excellent working, drying and binding properties.
Lampblack in oil in tubes is not called for by artists, but sign writers favor it put up in large tubes, as well as tin cans, under the brand, "Sign Writers' Black." Some makers simply grind lampblack in boiled linseed oil with a portion of drier, while others again grind gas carbon black in raw or boiled linseed oil with sufficient japan drier. The latter being more jet black is in favor as a ground for smalting black signs.