Bone black, made from calcined bones, is found on the market in several grades, that made from freshly calcined bones being purest and best in tone. Recovered bone black, known as sugar house black, is also calcined bone black, used for refining (bleaching) sugar, which if not properly washed contains vegetable matter that prevents the black from drying as well as the freshly calcined bone black. While cheaper, it is not a safe pigment for paint, and the bulk of it is really used, without having been washed for fertilizing purposes on account of its contents of phosphate of lime. Bone black is often confused with animal black, which, however, is an error, as bone black must not contain any other material but the charred bones, while animal black contains all the charred or calcined refuse of animal matter, such as hoofs, horns, hair, skins, bones, leather, etc. Animal black varies to a great extent in bulk, density, staining power and hue, while bone black made from freshly calcined bones shows very little variation in depth of tone, bulk or strength. Pure bone black very seldom shows more than 15 per cent carbon and 78 per cent of ash that consists of 60 to 62 per cent of phosphate of lime, the balance being carbonate of lime with traces of alumina and silica, sometimes also of iron. The color grinder will test bone black, which is usually offered under the name of powdered drop black, for fineness of texture, for tinting strength with white and for oil absorption. When bone black requires less than 45 per cent by weight of oil to 55 per cent of the dry powder to make a smooth paste it should be viewed with suspicion as to purity, and when black is offered under that name that requires over 50 per cent of oil to 50 per cent by weight of black it is either not pure bone black or contains free moisture. Any kind of black should be bone dry before mixing in order to grind freely and make a smooth paste, more especially when it is to be ground in japan or varnish. Pure bone black is preferred by many carriage painters on account of its tooth as against the softer imported ivory blacks, though where intense covering capacity is desired, as well as absence of the grayish hue, the denser animal blacks or bone black with the addition of gas carbon black is preferred. While the various government service branches in their specifications for drop black in oil insist on pure bone black for the pigment, very few color grinders are placing a black of this kind on the market under the drop black label, as they strengthen the bone black by the addition of some Prussian blue or gas carbon black. This applies to the oil black. As may be gleaned from the price lists on colors in oil, the black listed as coach or drop black is quoted at similar price and the consumer will find the same quality in the container, no matter whether the label reads drop black or coach black. Bone black is very slow drying in oil, and, where not bound by specifications, the color grinder will do well to use a vehicle consisting of good boiled linseed oil or of 95 per cent raw linseed oil and 5 per cent first-class oil dryer.