COLOURS, 
Veral sizes, reflect rays of one colour and 
transmit those of another, he lienee ob- 
serves, 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 consti- 
tute globules of all intermediate sizes, these 
globules are capable of reflecting some CO- 
lours, and transmitting 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 magnitude as to se- 
pai-ate these colours? And why are they 
rarely, if ever, seen tinctured with blue and 
green, as welt as red, orange, or yellow? 
Is it not more credible, that the separation 
of rays is made in passing through the hori- 
zontal atmosphere, 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 colour 
becomes still deeper after sun-set.” Hence 
he concludes that the clouds, according to 
their different altitudes, may assume all the 
variety of colours at siln-rising and setting, 
by barely reflecting the sun’s incident light 
as they receive it. 
Colour.?. This very important article 
includes a variety of matters of peculiar in- 
terest to various professions, and requiring 
no inconsiderable portion of study. We 
have only seven natural colours, namely, 
red, orange, yellow, green, blue, indigo, 
and violet. See Chromatics. 
The mechanical use of colours is more 
immediately under our present considera- 
tion. 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 object to which 
they are applied: these are again divided 
into oil and water colours. Transparent 
colours are made either of expressed juices, 
corrected by inspissation, or of the finer 
particles of earths, gums, &c. highly pre- 
p-oi-ed by levigation, washing, &c. 
Oil colours are made by mixing the co- 
louring substances witli 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 publication (the seventh 
number of the Agricultural Magazine) we 
are informed, that sun-flower oil possesses 
qualities of great moment to the painter, 
and to various other artists. The colouring 
matter must 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, without making 
allowance for some particular substances, 
especially minerals, which, however well 
they may have been prepared, will occasion 
a roughness to the touch. Body colours 
are usually sold in bottles, ready mixed to 
tiieir proper consistence, and sometimes 
in cakes, with a small portion of gum Ara- 
bic dissolved in the water. Oil colours are 
most frequently sold in kegs, and ready 
ground, but requiring an addition of oil be- 
fore they can be worked : these are gene- 
rally for the use of house painters, &c. s 
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 plastermg or concealing the 
paper, &c.: hence their designation. The 
best of every kind are made from either 
vegetable or animal substances; minerals 
being extremely difllicult to prepare, equally 
so to work with water, and many of them 
very subject to change. We shall give a 
concise account ot the materials in general 
use; observing, that there are an immense 
number of compound colours, sold under 
various names, that may be made from the 
following list of simples : 
REDS. 
Carmine, or the extract of cochineal. 
Excellent. 
Florentine lake, made fi om refuse cochi- 
neal, with a small addition of Brazil wood, 
precipitated by adding a solution of tin. 
Hoes not stand. 
Madder lake, the same as tlie foregoingj 
