Colour-Making, is the art of preparing various colours employed in painting. This art, tho one of the most curious branches of chemistry, is the least understood. The principles that govern it, differ totally from those, on which the theory of other parts of chemistry is founded; and as the practical part is in the hands of persons who sedulously conceal their methods of preparing colours, we have only a superficial theory, and are but imperfectly acquainted with the practice.

Colours are divided into various classes, such as opaque and transparent ; oil and water-colours; simple and compound , true and false.

I. Opaque colours are those which, when laid on any substance, efface every other painting or stain; such as white and red-lead, Vermillion, etc.. Transparent colours possess the peculiar property of leaving the ground, on which they are laid, visible through them. These are employed for illuminating maps, charts, etc.

II. Oil and water-colours are thus denominated, from their being appropriated to painting in oil, and in water.

In preparing oil-colours, care must be taken to grind them extremely fine ; and, when they are put on the pallet, to mix those which will not dry of themselves, with drying oils; and also to mix the tinged colours in as small quantitles as possible. With respect tome application of them, if employed for large pieces, they should be laid on full, in order that they may incorporate, and more firmly adhere. If they are intended to be glazed, particular care must be taken to paint the under-colour strong and smooth; after which the others may be gradually added, till the whole is properly filled up. Oil-colours are, however, sometimes worked dry, where only one is used, as in cameos, in which the gradations of colours of distant ob-jects are usuallymanaged by lights, as with crayons ; and in lasso relievos, which are imitations of sculpture, of every kind and colour.

Water-colours are wrought in various modes ; namely, in distemper (as artists express it),where the colours are prepared in size; in fresco or painting on fresh mortar, in which case it is requisite that the colouring be quick, lest the stucco or mortar dry, before it can be laid on; and that it be neatly and carefully executed ; each colour being properly placed, and occasionally intermingled by parcels: in agouache, where the colours are mixed with gum, and the pencil drawn along, as in paint and washings; and lastly, in miniature, for small and delicate works, in which the colours are required to be very fine and clean, to be mixed with gum, and worked in dots or points.

III. Simple and compound colours. The former are perfect in themselves, such as red and white lead, vermillion, the calces of iron, etc.; the latter are formed by the union of two or more colouring substances; for instance, blue and yellow, when blended together, make a green; red and yellow, an • orange; and white earth and cochi-neal, a lake, etc.

IV. The last and most important division of colours, is into true and false: the former retain their pristine tinge, without fading, un-der every possible variety of circumstances ; the latter either lose their colour entirely, or change into some other shade.

Colours are chiefly affected by being exposed to the sun during the summer, and to the cold air in winter. White lead, however, forms an exception ; as, when ground with oil, it retains its whiteness, if it be exposed to the weather, but degenerates into a brownish or yellowish cast, in a confined situation. Nevertheless, when it is immersed in water, it is totally divested of its colour, whether it be exposed to the eftects of the air or not. In the making of colours, the chief object is, that they may not fade, from the influence of the weather; though it must be regretted that the most beautiful are, in general, the least permanent. It may, however, for the most part be assumed, that the more simple any colour is, the less liable it will be to change by exposure to the air.

Having thus briefly stated the general theory of colours, we shall also give some account of the different pigments, which are most commonly employed by colour-makers.

1. Black, consists of several sorts, such as lamp-black, ivory-black, blue-black, and Indian ink. The first of. these is the finest of what are called soot-blacks, and is more used than any other. Its preparation depends on the manufacture of common resin. The impure juice collected from incisions made in pine, and fir-trees, is boiled down with a small quantity of water, and strained, while hot, through a bag; the dregs and pieces of bark, remaining in the strainer, are burnt in a low oven, whence the smoke is conveyed through a long passage into a square chamber, at the top of which is an opening, with a large sack affixed, made of thin woollen stuff: the soot, or lamp-black, concretes partly in the chamber, whence it is swept out once in two or three days, and partly in the sack, which is occasionally agitated, in order to take down the soot, and to clear the interstices between the threads, so as to admit a free current of air. This method of preparing lamp-black, was originally invented in Sweden, but has also been introduced into this country; and is now carried on to a considerable extent in the turpentine-houses, from die refuse of resinous matters.

Ivory -black is prepared from ivory, or bones, burnt in a close vessel; and, when finely ground, affords a deeper and more beautiful colour than lamp-black; but it is, in general, so much adulterated with charcoal, and so grossly levigated, as to be unfit for use. An opaque deep black, for water-colours, may be prepared, by grinding ivory-black with gum water, or with the aqueous liquid that settles from the whites of eggs, which have stood some time to subside.

Blue-black is said to be prepared from the burnt stalks and tendrils of vines. This is, however, seldom done by colour-makers, who generally substitute a mixture of ivory-black, and the common blue used for dveing cloths.

Indian-ink is an excellent black for water-colours, and consists of an equal mixture of lamp-black and common glue. Ivory-black, or charcoal, may be substituted for lamp-black; but it is seldom employed, on account of the great trouble of levigating it to a suffi-cient degree of fineness.

2. White, of which there are several kinds ; as flake - white, white-lead, calcined hartshorn, pearl-white, Spanish-white, egg-shell-white, and magistery of bismuth.

Flake-white, and white-lead, are the produce of the same metal. The preparation of the former is kept secret by colour-makers ; but the latter is made, by forming thin plates of lead into rolls, and placing them so as to imbibe the fumes of vinegar contained in a vessel, over a moderate fire. Nearly the whole is thus converted into a white calx, which is collected, ground up with water, and formed into little cakes. (See White-Lead.) - These two are the only whites that can be used in oil; all the rest being transparent, unless laid on with water.

Calcined hartshorn is the most useful of the earthy whites, as it contains the least proportion of alkali.

Spanish white is only chalk, very finely prepared.

Pearl-white is made from oyster-shells, as egg-shell-white also is from those of eggs. All these, from their attraction for acids, necessarily destroy those colours which are compounded with any acid or metallic salt.

The magistery of bismuth is ap to turn back, as well as flake-white, and white lead, when employed for a water-colour.

3. Red. The principal red colours used in painting, are car-mine, rose-pink, Vermillion, and red-lead.

Carmine is the brightest and most beautiful red colour known at present.—(See vol. i. p. 436).

Rose-pink is a very delicate colour, inclining more to purple than scarlet. It is prepared from chalk, coloured with a decoction of brasil-wood, heightened by an alkaline salt, which renders it very liable to fade, and of little value. This colour might be made more durable, by employing for its basis the white precipitate of lead ; and by brightening it with a solution of tin.

Vermillion consists of sulphur and quicksilver, the former of which is melted, when the quick-silver is stirred in, and the whole is converted into a black mass.— See Cinnabar, vol. i. p. 52/.

Red-lead is a calx, of a lively yellowish colour, which it acquires by slow calcination. Both these: colours are very durable ; the former, however, is the best red for oil-painting, but does not answer with water; the latter inclines to an orange ; and, like other preparations of lead, frequently turns black. 4. Orange. The genuine orange-coloured paints are, red 0rpi-ment, and orange-lake; the first of these is a sublimate formed of arsenic and sulphur; the other may be prepared from turmeric, infused in spirit of wine, having its colour struck upon ealx of tin, and brightened by a solution of that metal. The different shades of orange may, however, be pre pared by mixing red and yellow colours together in due proportions.

5. Yellow. - The chief colours of this kind are, Kings and Naples-yellow, Dutch-pink, and Tur-bith-mineral.

Kings-yellow is prepared from arsenic. Its colour is very beautiful, but apt to fade, on which account, as well as from its great price, it is but seldom employed.

The basis of Naples-yellow is had : it therefore frequency turns black; is particularly liable to be spoiled by iron, when moist, and should never come in contact with that metal, unless previously ground in oil.

Dutch-pink is said to be prepared by striking the colour of yellow berries upon chalk finely levigated. This, however, we doubt much, as its basis is harder and more gritty than chalk, and its colour more durable than others prepared in a similar manner.

Turbith-mineral is, at present, but little used in painting, though it appears to be very durable, and is there; ore preferable both to Kings and Naples-yellow.

6. Green. The only simple green of a tolerable degree of brightness, is verdigrease, or its different preparations : though far from being durable, it may be rendered more so, as a water-colour, by dissolving it in the pure tartarous acid. - A green colour may be made by compounding Prussian, or other blue, with yellow ; but it is by no means fixed, and much inferior to common ver-digrease.

7. Blue. The principal blue colours are, Prussian and Dutch Blue, Verditer, Smalt, Bice, and Indigo. Various processes have been adopted for the making of Pru sian-blue, of which we shall select the shortest.

Take 3 lbs. of dried ox's blood, 4lbs. 8oz. of quick-lime, 2lbs. of red tartar, and llb. 8oz. of saltpetre. Let them be calcined and lixiviated, when the lye should be poured into a solution of 4lbs. of alum, and 1 lb. of green vitriol. This operation will produce the finest blue; buttle quantity will exceed little more than 8oz. and 4 drams.

The preparation of verditer is studiously concealed, so that the best chemists of Europe have been baffled in discovering its component parts. It is very bright, and has a considerable tinge of green. This colour is durable in water; but, like verdigrease, dissolves in oil, and is subject to the same in-conveniencies.

Smalt is glass coloured with zaffre; a preparation from cobalt. It is, in general, so grossly pulve-rized as to be unfit tor painting, and its -texture is so hard, that it cannot easily be levigated. Its colour is exceedingly bright and durable ; and, if finely pulverized, is little inferior to Prussian-blue.

Bice is prepared from the Lapis Armenus, a stone which was formerly brought from Armenia, but now from Germany. Bice bears the best body of ail bright blues in common use, but it is the palest in colour. Being somewhat sandy, it is necessary to grind it very fine, and to wash it well, previously to its being used. It is as durable, and yields nearly as good a colour, as Prussian-blue.

Indigo is but little employed in, painting, either in oil, or water, on account of the dullness of the colour. It requires no other preparation than that of being washed over, before it is used. - See Indigo.

8. Purple. The only simple colour of this kind at present, is colcothar of vitriol, or crocus mortis. A beautiful purple lake maybe prepared from logwood, by-means of a solution of tin. As this mode of preparing colours is but little, known, we shall give a few hints respecting it, under the subjoined head of Colouring Matter.

9.. Brown. The chief Brown colours are bistre, and brown Pink. Bistre is prepared from the most glossy, and perfectly burnt soot, pulverized, passed through a fine sieve ; then baked in a little gum-water, and formed into cakes. This is a very useful colour in water, being exceedingly fine and durable, and not apt to spoil any other colours with which it is mixed. The brown-pink is said to consist of chalk, tinged with the colouring matter of fustic, heightened by fixed alkaline salts. It is, consequently, very perishable, and seldom used. - See also Chafer, vol, i. p. 486.

Colouring Matter is contained in almost every flower and root of vegetables, and may be extracted by a very simple process. The Dutch prepare pigments of the most beautiful shades, for instance, a very line azure blue, from the blossoms of the corn bluebottle, Centaurea Cyanus, L. - a delicate red, from the fresh leaves of roses, especially the small French rose ; - an excellent violet from the flowers of that name, etc. in the following manner : Take the roots, leaves, or flowers of whatever quantity is desired, bruise them nearly to a pulp, put them into a glazed earthen vessel, pour a sufficient quantity of filtred water over them, and add a table spoonful of a strong solution of pure pot-ash to every pint of the former. Boil the whole over a moderate fire, till the liquor is evidently saturated with the colour afforded by. the vegetable ; then decant the fluid part, either through blotting paper, or cloth, and gradually drop into it a solution of alum, when the colouring matter will subside at the bottom. This powder should again be washed in several fresh waters, till they pass away perfectly tasteless : at length, it must be once more fil-tred through paper, and the remaining substance perfectly dried. From this preparation are afterwards manufactured the finest pigments, or water-colours, of the shops, by triturating them on mar-ble stones, with the addition of a little clarified gum-water, and then forming them into cones, cakes, etc. Having already, under the different heads of plant, mentioned the various purposes to which they may be usefully applied, in the arts of colouring, dyeing, tanning, etc. it would be superfluous to enumerate them on this occasion - 3 task we are necessarily obliged to defer, on account of the great va-riety of vegetables which will occur in the sequel of the alphabet. To enable, however, those readers who are engaged in any particular art, or trade, to take a comprehensive view of every useful fact con-nected with their respective pursuits, we take this opportunity of informing them, that we intend to give a copious and universal Index of Reference, at the conclusion of our labours. By the assistance of such an index, they will be enabled immediately to avail themselves of all the modern improvements, discoveries, and inventions, relative, to any subject treated of in the Do-mestic Encyclopaedia; whether it he recorded under a distinct head of the alphabet, or only incidentally mentioned.