COLOURS. 



applied to the cloth without the interven- 

 tion of any mordant. To one or other 

 of the foregoing classes may be referred 

 all the colours used in calico-printing 1 , 

 with the exception, however, of those sys- 

 tems of colours which have been pro- 

 duced by calico-printers in this country, 

 within a short period, by processes and 

 upon principles which have hitherto not 

 been made known. See 



COLOUR of the clouds is thus accounted 

 for by Sir Isaac Newton. Concluding", 

 from a series of experiments, that the 

 transparent parts of bodies, according to 

 their several sizes, reflect rays of one co- 

 lour, and transmit those of another, he 

 hence observes, that when vapours are 

 first raised, they are divided into parts 

 too small to cause any reflection at their 

 surfaces, and therefore do not hinder the 

 transparency of the air ; but when they 

 begin to coalesce, in order to form drops 

 of rain, and constitute globules of all in- 

 termediate sizes, these globules are capa- 

 ble of reflecting some colours, and trans- 

 mitting others, and thus form clouds of 

 various colours, according to their sizes. 

 Mr. Melville controverts this doctrine, in 

 its application to the red colour of the 

 morning and evening clouds. " Why," 

 he says, " should the particles of the 

 clouds become at that particular time, 

 and never at any other, of such a magni- 

 tude as to separate these colours ? And 

 why are they rarely, if ever, seen tinc- 

 tured with blue and'green, as well as red, 

 orange, or yellow ? Is it not more credi- 

 ble, that the separation of rays is made in 

 passing through the horizontal atmo- 

 sphere, and that the clouds only reflect 

 and transmit the sun's light, as any half- 

 transparent colourless body would do ? 

 For since the atmosphere reflects a greater 

 quantity of blue and violet rays than of the 

 rest, the sun's light transmitted through it 

 ought to incline towards yellow,orange,or 

 red ; especially when it passes through a 

 long tract of air: and thus it is found, that 

 the sun's horizontal light is tinctured with 

 a deep orange, and even red; and the co- 

 lour becomes still deeper after sun-set." 

 Hence he concludes that the clouds, ac- 

 cording to their different altitudes, may 

 assume all the variety of colours at sun- 

 rising and setting, by barely reflecting 

 the sun's incident light as they receive it. 



COLOURS. This very important article 

 includes a variety of matters of peculiar 

 interest to various professions, and re- 

 quiring no inconsiderable portion of study. 

 We have only seven natural colours, 



namely, red, orange, yellow, green, blue, 

 indigo, and violet. See CHROMATICS. 



The mathematical use of colours is more 

 immediately under our present conside- 

 ration. These are either what are called 

 body, or transparent : the former applies 

 to such as have a certain substance, being 

 like very thin paste, and coating the ob- 

 ject to which they are applied: these are 

 again divided into oil and water colours. 

 Transparent colours are made either of 

 expressed juices, corrected by inspissa- 

 tion, or of the finer particles* of earths, 

 gums, 8cc. highly prepared by levigation, 

 washing, &c. 



Oil colours are made by mixing the co- 

 louring substances with prepared oils; 

 that is, such as dry readily, and are at the 

 same time so fine and transparent as not 

 to injure the brilliancy or clearness of 

 the colour. Nut-oil is on this account 

 highly esteemed ; but in a recent publi- 

 cation (the seventh number of the Agri- 

 cultural Magazine) we are informed, that 

 sun-flower oil possesses qualities of great 

 moment to the painter, and to various 

 other artists. The colouring mattermust 

 be minutely mixed with the oil, so that it 

 may work perfectly free and smooth. 



Body colours for the limner's use should 

 be prepared of the purest materials, and 

 be triturated in a mortar, and on a slab 

 with water, until such time as the mixture 

 is completely smooth,and leaves no rough- 

 ness when rubbed between the thumb and 

 fore-finger: not, however, withoutmaking 

 allowance for some particular substances, 

 especially minerals, which, however well 

 they may have been prepared, will occa- 

 sion a roughness to the touch. Body co- 

 lours are usually sold in bottles, ready 

 mixed to their proper consistence, and 

 sometimes in cakes, with a small portion 

 of gum Arabic dissolved in the water. 

 Oil colours are most frequently sold in 

 kegs, and ready ground, but requiring an 

 addition of oil before they can be work- 

 ed : these are generally for the use of 

 house painters, &c. : those for the more 

 delicate purposes are usually kept in 

 bladders. 



Transparent colours should be so clear, 

 when mixed with abundance of water, as 

 to communicate a strong tint, without in 

 the smallest degree plastering or conceal- 

 ing the paper, &c. : hence their designa- 

 tion. The best of every kind are made 

 from either vegetable or animal substan- 

 ces ; minerals being extremely difficult to 

 prepare, equally so to work with water, 

 and many of them very subject to change. 

 We shall give a concise account of the 



