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used as a water-colour as to show a great variety of tints and shades; it is this property which makes it of value for monochrome work to artists; no other pigment is capable of being used in this manner with so much facility.

Sepia is a compound of calcium and magnesium carbonates, with an organic colouring principle; Prout has analysed it, and gives its composition as

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The black pigment may be isolated by boiling the bag, first in water, which takes out the alkaline salts; then in hydrochloric acid, which takes out the calcium and magnesium carbonates; then, after washing with water, filtering, and drying, the pigment is ready for use.

Sepia is a fairly permanent pigment, being but little affected by exposure to light and air. It is not altered by admixture with any other pigment.

CAPPAGH BROWN.

This pigment is of a reddish-brown hue, and much resembles raw umber both in appearance and composition. It is found at the Cappagh Mines of Lord Audley, which are situated about 10 miles from the town of Skibbereen, in the county of Cork. Prof. A. H. Church gives the following analysis of Cappagh

brown :

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There were traces of organic matter, but not enough to show

that it had been derived from bog earth or peaty matter.

* Church, Chemistry of Paints and Painting, p. 206.

It is

possible that part at least of the manganese, if not the whole of it, existed in the pigment in the form of the red oxide, Mn, O4 When heated above 100° C. it acquires a rich red colour not unlike that of burnt sienna.

Cappagh brown works well in oil- or water-colour, and is a permanent pigment. Its qualities as an oil colour are much improved by a preliminary drying at a temperature not exceeding 75 to 80° C. It has been much used by artists since its

introduction.

ganese.

MANGANESE BROWN.—This brown is an oxide of manIt is prepared artificially from the waste still-liquors of the chlorine manufacturer, by precipitating these with sodium carbonate, collecting the precipitate, and calcining in a furnace to a low red heat, until samples taken out and allowed to cool show that the pigment has acquired the desired shade. It is a good and permanent pigment, but it has such excessively-strong drying properties as to make it very unusable as a pigment; hence it has gone out of use. The manufacture of manganesebrown was patented in 1871 by Rowan.

COLOGNE EARTH, CASSEL EARTH, RUBENS BROWN, and other browns are pigments of natural origin of varied composition; some partake of the character of brown lignite of a soft character, others more nearly resemble the umbers in their composition. Their value as pigments is very variable, and, as their composition cannot be depended upon as being constant, it is advisable to avoid the use of these pigments for all artistic painting.

BONE-BROWN is made by gently calcining bones until they acquire a brown colour; it resembles bone-black in composition, but contains some undecomposed animal matter; it is not much used.

PRUSSIAN BROWN.-This pigment is rarely met with now. It was prepared by gently calcining Prussian blue, and hence is a mixture of ferric oxide and carbon; necessarily the pigment was a costly one, and it has no advantage over such pigments as umber or Vandyke-brown.

BISTRE.-This pigment is prepared from the soot of wood, especially from that of beech wood, which gives the finest quality. The soot is collected and washed with hot water until the latter does not extract any more soluble matter from it; sometimes the soot is subjected to a preliminary grinding before the washing. The bistre is dried, and is then ready for use. Bistre is not used as an oil-colour. It has a fine warm brown colour of a yellowish hue. Its permanence depends very much

on the character of the wood-soot from which it is made; sometimes this contains much tarry matter which is not completely extracted from the bistre by the washing operation; the larger the quantity present in the bistre the more fugitive is the pigment. The tarry matter oxidises on exposure to light and air, and the tint becomes, in consequence, paler.

ULMIN BROWNS are pigments made by heating organic matter with alkalies; they are not used, as they are too fugitive. ASPHALT or BITUMEN OF JUDEA was used as a pigment by many of the older artists; but, as time has brought out its many defects, artists have ceased to use it. It enters very largely into the manufacture of varnishes-partly as a colouring matter, partly as a resinous matter. It is described in the section on varnish materials.

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NEARLY all the black pigments in use, certainly all those which are most used, are composed either of carbon itself or have that element as their colouring principle. Although carbon exists naturally, yet its native form is not used as a pigment in painting, as it lacks the properties required for that purpose; therefore all the black carbon pigments are made artificially.

Such carbon-blacks are known under a variety of names; lampblack, vegetable black, carbon-black, are almost, especially the last two, pure carbon; animal-black, bone-black, ivory-black, drop-black, Frankfort black, are blacks prepared from animal and vegetable matters, and contain various other constituents besides carbon.

Besides the pigments just named, and which are specially prepared for use as pigments, carbon is also obtained in other forms, such as coke, charcoal, soot, &c. Some of these are more or less black, and they have been proposed for use as pigments after being subjected to grinding and washing, but they do not make good pigments, and it is doubtful whether they are so used at the present time. Certain natural minerals, such as coal and carbonaceous shale, have also been proposed to be used as pigments, but, as with those just noted, the proposal has probably never been put into practical use.

Carbon is an elementary body belonging to the group of nonmetals; its chemical symbol is C, and its atomic weight 12. It is a combustible body in all its forms; in burning it combines with oxygen to form carbon dioxide (carbonic acid gas), CO2, whence it follows that all the black pigments of which carbon forms the principal or only constituent are combustible; a fact which sometimes makes itself apparent in a disagreeable form during the process of manufacture. It is a perfectly stable element, and will remain unaltered by exposure to the atmosphere for any length of time.

Acids and alkalies have no action on carbon. All forms of

carbon-blacks are perfectly permanent pigments, and are unsurpassed in permanency by any other pigment. They can be mixed with all other pigments without bringing about any alteration. Some of the blacks have slight peculiarities, as will be noticed in the descriptions of them.

LAMP AND VEGETABLE BLACKS.

These two pigments are closely allied as regards the method of their preparation and their composition; as a matter of fact they are made together at the same time and by the same operation. Lamp-black is probably the most common and most used of the black pigments. Essentially it is a kind of soot. Whenever a combustible body, such as an oil, or fat, or grease, is burnt under such conditions as to preclude complete combustion, then a large volume of smoke is produced, and this deposits a black soot on any surface it may come in contact with; such soot has a strong black colour and is highly prized as a pigment. Owing to the fact that the earliest convenient means of producing this black was by burning the oil in a lamp under conditions, easily attained, which would ensure that the combustible would not be completely burnt, the black has derived its name of lamp-black. Very little lamp-black is now made by burning oil in a lamp, partly because materials are now used in its preparation which cannot be burnt with good results in a lamp.

The materials used in the manufacture of lamp and vegetable blacks are very varied, and comprise all kinds of oils, fats, coaltar oils, and greases; in fact, anything that will yield a great deal of black smoke while burning, preference being given to those which are cheapest and least available for any other purpose. There are some differences in the quality of the blacks yielded by the different kinds of materials used; the fatty oils and greases yield the best blacks; the hue is better and the black is finer and less greasy than that from any other kind of grease. The greases from coal-tar give fair blacks; they are rather browner in hue than the blacks from the fatty oils, and more inclined to be oily from some of the material volatilising at the high temperature at which it is burnt. The residues from the distillation of shale give fair blacks, but are liable to contain traces of volatile unburnt matter. This oily volatile matter in the blacks from coal-tar and shale greases has the effect of causing the black to be a bad drier when used as an oil-paint.

The process of manufacture of lamp-blacks consists essentially in burning the material and collecting the soot. The plant

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