White Chalk





Is a well-known native carbonate of lime, employed by the artist only as

a crayon, or for tracing his designs, for which purpose it is sawed into

suitable lengths. White crayons and tracing chalks, to be good, must

work and cut free from grit. From this material are prepared whitening

and lime, which form the bases of many cheap pigments and colours, used

in distemper, paper-staining, &c.



Besides those mentioned, there are other metallic whites varying in

beauty and opacity, such as those of mercury, arsenic, and antimony; but

none of them are of any value or reputation in painting, on account of

their great disposition to change of colour, whether by light or foul

air, both in water and oil.



There are also other terrene whites, under equivocal names, among which

are Morat or Modan white, Spanish white, Troys or Troy white, Rouen

white, China white, and Satin white; the latter being a sulphate of lime

and alumina, which dries with a glossy surface. The common oyster-shell

contains a soft white in its thick part, and there is the white of

egg-shells. There is, too, an endless variety of native earths, in

addition to those prepared by art. The whole of them, however, are

destitute of body in oil; and several, owing to their alkaline nature,

are injurious to many colours in water, as well as to all colours which

cannot be employed in fresco.



Among the infinitude of white substances, the artist finds that there

are but three white pigments--those of lead, zinc, and baryta. The first

possesses the greatest opacity, while the second and third are most

durable. The last, however, has so many objectionable qualities, that

the number of eligible whites, may almost be said to be two--lead and

zinc. Of these, the former is blackened by foul air, and in oil, the

latter is wanting in body. In fact, there is but one white pigment which

approaches perfection--Chinese white; and this is only a water-colour.












TTITLE ON THE PRIMARY YELLOW



Yellow is the first of the primary or simple colours, nearest in

relation to, and partaking most of the nature of, the neutral white; it

is accordingly a most advancing colour, of great power in reflecting





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