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Carbon

grains, gelatine, water, black, red, mixture and lake

CARBON TISSUE.—Paper coated with gelatine containing one or more pigments, and used in the carbon process, q.v.

The composition of the pigments used should be carefully studied. If carbon lampblack only is used, we get pictures that will last a long time, as proved by the brilliancy of printers' ink many years old. But it is nearly always necessary to add some other color to give an agree able tone. The colors of the pigments used depend, of course, upon the kind of picture to be reproduced. For instance, if it is intended to reproduce a red-chalk drawing, by incorporating with the gelatine a pigment of the same color, an almost perfect may be obtained. To manufacture carbon tissue requires too much labor to be profitable to any but very large con sumers. The Autotype Company manufacture their tissue. and sell the same plain or sensitized. This tissue may be obtained to give pictures of the following tints:—Standard brown, engraving black, sepia, red chalk, standard purple, warm black, portrait brown, portrait purple, special purple, sea green, and a special for transparencies.

A good carbon paper may be made as follows: Gelatine 5 ounces Isinglass S4 onnce Water 7o ounces Lampblack )‘ ounce English red (peroxide of iron) i ounce Glycerine i 4 ounces Dr. Gunther gives this formula, and describes the method of preparing it as follows:—The gelatine should be neither too soft nor too cold, and the quantity of glycerine should be about equal to the volume of the coloring matter added. The black color is rubbed down on a stone slab, then the glycerine is added and the rubbing continued. Sufficient water is then poured on to obtain the required consistency, and the desired degree of fineness having been certain, the color is collected with a horn spatula. The red color is rubbed down with water only. The two colors are then mixed together on the slab. During the time occupied in preparing the colors, the isinglass, cut into small pieces, is allowed to soak in about 4 ounces of water. It is then boiled, stirring all the time, until but fine skins are floating in the somewhat muddy solution, when the whole is strained through linen. This solution

is then poured into the gelatine, previ ously dissolved in lukewarm water. The coloring matter is now placed in a large porcelain dish, and the warm gelatine and isinglass solution added in small quantities, stirring all the time with a pestle until an even homo geneous mixture has been produced. The whole is at once strained through muslin or moistened flannel, and the mixture is ready for coating. For methods of coating paper with gelatine see Coating.

The plain paper should be tough and have a smooth surface. It must not be too strongly sized, as it requires to be readily permeated by the water when developing.* A gelatine should be used that is neither too hard nor too soft. As a rule, a mixture of the two kinds is employed.f In choosing the coloring matter only those that are permanent should be used. Liesegang gives the following:I Brown tones are obtained with caramel, dark oxide of iron, Indian red and carmine lake. Purple tones with artificial alizarine and purpurine dissolved in caustic soda.

Warm black tones with mixtures of indigo. umber and carmine lake.

tones, with a mixture of Vandyke . - - • • -• brown, two grains; Venetian red, three grains; indigo, one grain; carmine lake, one grain; bone black, fifteen grains. with a mixture of China ink, three grains; carmine lake, four grains; Vandyke brown, four grains.

Photographic tones, with Indian ink, four grains; carmine lake, three grains, and Indian red, five grains.

For old engraving reproductions, sepia by itself, or mixed with a little bone black, can be employed.

Liesegang gives the following as suitable proportions for the gelatine mixture: Water 1 onuce Gelatine 120 to 150 grains Soap 15 grains Sugar.... 21 grains Dry coloring matter 4 to 8 grains large glass bottle enclosed in a box or basket. It is used for holding solutions, particularly cor rosive acids.

CARBOY arrangement for holding a carboy, to facilitate the pouring out of the liquid. (Fig. 95.) CARCEL standard lamp used in photo metry. It is equal to 9a candles.