Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/52

34] indicates a harsh, nauseous, and disagreeable taste; as in the berries of deadly night-shade, myrtle-leaved sumach, herb-christopher, and others; many of which are not only unpleasant to the taste, but pernicious and fatal in their effects.  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, &c. 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, &c.

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 quantities as possible. With respect to the 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 objects are usually managed by lights, as with crayons; and in basso 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, vcrmillion, the calces of iron, &c.; the latter are formed by the union of two or more colouring substances; for instance, blue and yellow, when blended together, make