When intended for use as a deodoriser or decoloriser, bone-black should be kept carefully excluded from the air, for by exposure it loses this power to a great extent, and becomes almost inert. That which has been freshly burned is therefore best for these purposes.
The cost of production of bone-black may be calculated as follows:—
| £ | s. | d. | |||||
| 4 tons fat bones at 4s. per cwt | 16 | 0 | 0 | ||||
| 27½ bushels coals | 1 | 3 | 9 | ||||
| 2 firemen | 0 | 4 | 9 | ||||
| 4 workmen | 0 | 8 | 0 | ||||
| 1 carman | 0 | 2 | 4 | ||||
| 2 horses | 0 | 5 | 7 | ||||
| Breaking up the bones | 1 | 5 | 4 | ||||
| Rent and taxes | 0 | 8 | 0 | ||||
| Interest, repairs, and wear and tear | 0 | 7 | 2 | ||||
| Contingencies and transports | 0 | 2 | 4 | ||||
| £20 | 7 | 3 | |||||
| Produce:— | |||||||
| Black, 60 per cent., say 38 cwt. in grains, at 14s. 3d. | 13 | 10 | 9 | ||||
| 10 cwt. fine, at 5s. 6d. | 1 | 7 | 8 | ||||
| Fat, 6 per cent., say 5 cwt., at 31s. 8d. | 7 | 18 | 4 | ||||
| £22 | 16 | 9 | 22 | 16 | 9 | ||
| Profit | £2 | 9 | 6 | ||||
Bone-black never has the depth or brilliancy of lamp-black, but it mixes well with either water or oil, and though a slow drier as an oil paint, is permanent and not high priced.
Frankfort-black or Drop-black.—This is a black powder obtained from dried vine-twigs carbonised to a full black and then ground very fine. On a large scale it is prepared from a mixture of vine-twigs, wine-lees, peach-stones, bone-shavings, and ivory refuse. It varies in shade according as the animal or vegetable charcoal is in excess; when the latter predominates, the powder is of a bluish colour; but when there is an excess of animal charcoal, it has a brownish tinge. It is customary to wash the powder well when first made, in order to remove any soluble inorganic impurities. The finest Frankfort-black is probably the soot obtained from the combustion of the materials mentioned above. It makes an excellent pigment, and is extensively used by copperplate engravers in the preparation of their ink. Drop-black is simply Frankfort-black ground exceedingly fine, mixed with a little glue water, and dried in pear-shaped drops for sale.
Ivory-black.—Ivory-black is a beautiful black pigment prepared by carbonising waste fragments and turnings of ivory. These are exposed to a red heat for some hours in crucibles, great care being taken to avoid overheating or burning. When quite cold, the crucibles are opened, and the contents are pulverised, the richest coloured fragments being kept apart for the best quality. The powder is then levigated on a porphyry slab, washed well with hot water on a filter, and dried in an oven at a temperature not exceeding 212° F. The product is of a very beautiful velvety black colour, superior even to that obtained from peach-kernels, and quite free from the reddish tinge which so often characterises bone-black. Ivory-black, like Frankfort-black, is employed by copperplate printers in the preparation of their ink. Mixed with white lead, it affords a rich pearl-grey pigment.
Lamp-black.—Lamp-black is an exceedingly light, dull-black powder, formed by the imperfect combustion of oils, fats, resins, &c. It may be prepared on a small scale by suspending a small tin-plate funnel over the flame of a lamp fed with oil, tallow, or crude naphtha, the wick being so arranged that it shall burn with a large and smoky flame. Dense masses of this light carbonaceous matter gradually collect in the funnel, and may be removed from time to time. The funnel should be furnished with a metal tube to convey the gases away from the room, but no solder must be used in making the connections.
Figs. 3 and 4.—Apparatus for making Lamp-black.