A New Supplement...: Oil Colours.

A New Supplement to the latest Pharmacopoeias of London, Edinburgh, Dublin, and Paris, Forming A Complete Dispendatory, Conspectus, and Dictionary of Medical Chemistry, Giving All the Old and New Names, Including the New French and American Medicines, and Poisons; with Symptoms, Treatment, and Tests; as Well As Herbs, Drugs, Compounds, Veterinary Drugs, With the Pharmacopoia of the Vetenary College, Nostrums, Patent Medicines, Perfumery, Paints, Varnishes, And similar articles kept in the Shops; With Their Compositions, Imitations, Adulterations, And Medicinal Uses, Being a General Book of Formulæ and Recipes For Daily Reference in the Laboratory and at the Counter.
Fourth edition, corrected, improved, and very much enlarged.
By James Rennie, M. A., Editor of the Quarterly Journal of Foreign Medicine; the Pharmacopeia Universalis; Author of a Conspectus of Prescriptions in Medicine, Surgery, and Midwifery; the Pharmacopeia Imperialis, &c. &c.
London: Baldwin and Cradock. 1837.
London: Thomas Curson Hansard, Paternoster Row.

OIL COLOURS, for artists, ought to be brilliant, clear, and permanent, as pictures soon lose their value when painted in perishable colours. Some of the Egyptian paintings remain unchanged in tint after 2000 years; while some of the pictures of Sir Joshua Reynolds have not stood 40 without fading. The following are a few of the chief oil colours, and the methods of preparing them:

Azure. Take 3ij of quicksilver, 3ss each of sulphur and hydrochlorate of ammonia; grind all together, and put the contents to digest in a matrass over a slow fire, increase the heat a little, and when an azure fume arises take the matrass from the fire. When cool, these will make as beautiful an azure as ultramarine.

Liquid Blue. Put into small matrass, or phial, 3j of fine percyanide of iron (prussian blue), reduced to powfer, and pour over it from 3ss to 3ij of concentrated hydrochloric acid. The mixture produces an effervescence, and the percyanide soon assumes the consistence of thin paste. Leave it in tthis state for 24 hours, then dilute i t with 3viij or 3ix of water, and preserve the colour thus diluted, in a bottle well stopped. The intensity of thic colour may be lessened, if necessary, by the addition of water. If the whole of this mixture be poured into aq quart of water, it will still exhibit a colour sufficiently dark, for washing prints. This colour, charged with its mordant, requires the use of gum water made of gum tragacanth. Mucilage of gum arabic does not possess sufficient consistence.

Blue Verditer. Into lb100 of whiting pour copper water, and stir them together for some hours, till the water grows pale; then pour that away, set it by for other use, and pour on more of the green water, and so till the verditer be made, which, being taken out, is laid on large pieces of chalk in the sun, till it be dry and fit for market.

Saxon Blue, may be successfully imitated by mixing with a divided earth percyanide of iron, at the moment of its formation and precipitation. Into a solution of 144 grains of sulphate of iron pour a solution of ferrocyanide of potassium; at the time of the formation of the percyanide of iron, add, in the same vessel, a solution of 3ij of alum, and pour in with it the solution of ferrocyanide of potassium, just sufficient to decompose the sulphate of alumine; for alkali in excess might alter the percyanide of iron.
It will therefore be much better to leave a little alum, which may afterwards be carried off by washing. As soon as the alkaline liquor is added, the alumine precipitated becomes exactly mixed with the percyanide of iron, the intensity of which it lessens, by bringing it to the tone of common Saxon blue. The matter is then thrown on a filer, and, after being washed in clean water, is dried. This substance is a kind of blue verditer, the intensity of which may vary according to the greater or less quantity of the sulphate of alumine decomposed. It may be used for painting in distemper.

Dutch Pink from Wood. Boil the stemps of wood in alum water, and then mix the liquor with clay, marl, or chalk, which will become charged with the colour of the decoction. When the earthy matter has acquired consistence, form it into small cakes, and expose them to dry. It is under this form that the Dutch pinks are sold in the colour shops.
The small blackthorn produces a fruit, which, when collected green, are called yellow berries. The seeds, when boiled in alum water, form a Dutch pink superior to the former. A certain quantity of clay or marl is mixed with the decoction, by which means the colouring part of the berries unites with the earthy matter, and communicates to it a beautiful yellow colour.
Or, by substituting for clay a substance which presents a mixture of clay and metallic oxide; the result will be a Dutch pink of a very superior kind. Boil separately lbj of yellow berries, and 3iij of the alum, in lbxij of water, which must be reduced to lbiv; strain the decoction through a piece of linen, and squeeze it strongly; then mix up with it lbij of ceruse, finely ground on porphyry, and lbj of pulverized Spanish white; evaporate the mixture till the mass acquire the consistence of a paste, and  having formed it into small cakes, dry them in the shade. When these cakes are dry, reduce them to powder, and mix them with a new decoction of yellow berries. By repeating this process a third time, a brown Dutch pink will be obtained. In general the decoctions must be warmed when mixed with the earth. They ought not to be long kept, as their colour is speedily altered by fermentation; care must be taken also to use a wooden spatula for stirring the mixture. When only one decoction of wood or yellow berries is employed to colour a given quantity of earth, the Dutch pink resulting from it is of a bright yellow colour, and is easily mixed for use.  When the colouring part of several decoctions is absorbed, the composition becomes brown, and is mixed with more difficulty, especially if the paste be argillaceous, for it is the property of this earth to unite with oily and resinous parts, to adhere strongly to them, and incorporate with them. In the latter the artist must not be satisfied with mixing the colour, it ought to be ground, an operation equally proper for every kind of Dutch pink, and even the softest, when destined for oil painting.

Yellow Lake. Take lbj of turmeric root in fine powder, three pints of water, and 3j of carbonate of potass, put all into a glazed earthen vessel, and boil them together over a clear gentle fire till the water appears hightly impregnated, and gives a stain  of a beautiful yellow; filter this liquor, and gradually add to it a strong solution of roche alum in water, till the yellow matter is all curdled and precipitated. After this, pour the whole into a filter of paper, and the water will run off, and leave the yellow matter behind; wash it with fresh water till the water comes off insipid, and then is obtained the beautiful yellow called  lacque of turmeric.

Another Yellow Lake. Make a lye of potass and lime sufficiently strong; in this boil gently fresh broom-flowes, till they  are white; then take out the flowes, and put the lye to boil in earthen vessels over the fire, add as much alum as the liquor will dissolve, then empty this lye into a vessel of clear water, and it will give a yellow colour at the bottom; settle, and decant off the clear liquor, wash this powder which is found at the bottom, washed off, then separate the yellow matter, and dry it in the shade.

Lemon Yellow. A beautiful lemon colour may be formed by following the prescriptions of the old painters, who mix together the sulphuret and sesqui-suplhuret of arsenic (realgar and orpiment); but these colours, which may be imitated in another manner, have the disadvantage of being of a poisonous quality. It will therefore be better to substitute in their room Dutch pink of Troyes, and Naples yellow. This composition is proper for distemper, and for varnish; when ground and mixed the result will be a bright solid colour, without smell, if an alcoholic varnish be applied for the last coating.

Naples Yellow. There are two processes given for making this colour; first, lbj of antimony, lbj½ of lead, 3j of alum, and 3j of chloride of sodium; second, 3jss of pure ceruse, 3ij of peroxide of antimony, 3ss of calcined alum, and 3j of pure hydrochlorate of ammonia. THe ingredients are to be well mixed together, and calcined in a moderate heat for three hours, in a covered crucible, till it becomes nbearly red-hot, when the mass will become of a beautiful yellow colour; with a larger proportion of oxide of antimony, and hydrochlorate of ammonia, the yellow verges towards gold colour. Glass may be tinged yellow with the above preparation.

Patent Yellow. It is prepared by triturating minium or red oxide of lead and chloride of sodium together, and then exposing in a crucible to a gentle heat.

Under the words LAKE, CARMINE, PRUSSIAN BLUE, VERMILION, &c., I have given the methods of preparing other colours, used by painters.

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