THE TYPE, OR STANDARD, OF COLOUR.

To avoid misapprehension when speaking of colours, it is necessary to refer to some invariable type or standard of colour, so that when speaking of Blue, we may not be in doubt as to whether the colour represented by Prussian Blue, or by Cobalt Blue is meant. This type, or standard, is supplied by nature in the prismatic spectrum, andalthough in a weaker degree-in the rainbow. Therefore, whenever we speak of pure colours, those representing the colours of the spectrum must be understood. They are called also normal colours.

ON THE MIXTURE OF COLOURS.

We must never lose sight of the fact, that the results predicated of the mixture of colours, taken theoretically, are not obtained by mixing pigments, or paints, and dyes.

Theoretically, the mixture, or combination of the colours of the prismatic spectrum, by means of a lens or concave mirror, produces a ray of white light; but when we mix pigments representing those colours, taken as pure as we can possibly obtain them, the mixture is not white, but grey or black, according to their intensity, &c.: For every Blue pigment contains also either red or yellow;

Every Red pigment contains also either blue or yellow;

Every Yellow pigment contains also either blue or red. And although, as we have said, the union of the blue, red, and yellow of the spectrum produces white, the union of blue, red, and yellow pigments produces grey or black.

If we had pigments that were in colour as pure as those of the spectrum, their mixture would also yield pure colours.

Ultramarine is the only pigment that approaches a prismatic colour in its purity, but even that has a slight tinge of red in its composition, causing it to appear violet.

We can take gamboge as the representative of pure Yellow, carmine as that of Red, and Prussian blue as that of Blue.

In mixing pigments to obtain pure secondary colours, we shall obtain a better result if we select such as are free from the colour not essential to the compound. Thus, to obtain a pure green, which consists of blue and yellow only, we must take a blue tinged with yellow rather than with red, and a yellow tinged with blue rather than with red; if we took either of those pigments tinged with red, a quantity of black would be formed by its mixture with the two other primaries, and the green would be tarnished or broken. So long as pure blue

and yellow are mixed together, in varying proportions, but without the addition of the other primary colour (red), the resulting compound colour, green, remains a pure colour. Such is the theory, and the practical result is the same if the pigments we select to form the mixture are both free from the third primary.

When the three primaries (pigments) are mixed together in equal strength and proportions, the resulting compound is black. But if they are mixed in unequal strength and proportions, the mixture is grey, coloured by the primary or the secondary in excess in the Compound.

Normal Grey is formed by mixing a black with a white pigment in varying proportions, producing various tones of Grey.

By adding a primary or a secondary to normal Grey, we produce a coloured Grey.

There are as many classes of Grey as there are primary and secondary colours, and as many hues of Grey as there are hues of these pure colours. What are commonly called Tertiaries, are, in fact, coloured Greys: thus, Russet is red-grey, Citrine is yellow-grey, Olive is bluegrey.

If the primaries are mixed in unequal proportions, or are of different intensities, the mixture is a grey :

If the blue is in excess, the mixture is a blue-grey.

If the red is in excess, the mixture is a red-grey.

If the yellow is in excess, the mixture is a yellow-grey.

If the blue and the red are in excess, the mixture is a violet-grey. If the blue and the yellow are in excess, the mixture is a greengrey.

If the yellow and the red are in excess, the mixture is an orange

grey.

When two secondaries are mixed together the grey that results is coloured by the primary which enters into the composition of both secondaries, thus:

In mixing Green with Violet, the Grey is coloured by Blue, that being the primary in excess.

In mixing Green with Orange, the Grey is coloured by Yellow, being the primary in excess.

Green consists of Blue and Yellow
Orange consists of Red and Yellow

that

The compound contains twice as much Yellow as Blue or Red.

In mixing Violet with Orange, the Grey is coloured by Red, that

being the primary in excess.

It is understood that the colours employed are of equal strength and proportions.

COLOURS ARE MODIFIED IN HUE AND INTENSITY.

When one pure colour is added to another pure colour, in increasing proportions, we obtain hues of the colour receiving that addition.

Thus we may add to pure blue increasing quantities of red or of yellow, and so long as the blue predominates, the compound is a hue of blue; but so soon as the red or the yellow predominates in the mixture, it passes into a hue of red or of yellow.

Thus, proceeding from pure Blue, by adding yellow we obtain various hues of Yellowed blue, until we arrive at blue-Yellow, or Green. Any further addition of yellow carries the Blue into the yellow hues, and we have bluish-yellows until at length we arrive at pure yellow.

On the other side, by adding to pure Blue increasing quantities of Red, we obtain various hues of reddened blue until we arrive at bluered, or Violet; any further addition of red carries the blue into the red hues, and we have bluish-reds, until at length we arrive at pure red.

TONES.

When we add to a pigment, taken at its greatest intensity, increasing portions of white, which weakens its intensity, and of black, which deepens it, we produce various Tones of that colour.

It is understood that the pigment must be taken pure, and free from the admixture of grey or black. In the Rainbow, we find the colours of the prismatic spectrum, but of a lighter or weaker tone.

It is usual to call the weak tones of a colour tints, and the deep tones shades, but very often the word hues, is indiscriminately applied to those modifications of a colour.

Greater precision, therefore, in the language of colours, will be obtained by limiting the term tones to the modifications a colour undergoes by the addition to it of white or of black, producing a series of tones, light and dark. The term hues must be limited to the modifications a pure colour experiences when varying portions of another pure colour are added to it. If the colours are rendered impure by the presence of the third primary, they become broken colours or greys.

LUMINOUS AND SOMBRE COLOURS.

Colours are classed as warm or cold, according as they are luminous or sombre.

The luminous colours are Yellow, Orange, Red, and light Green. The sombre colours are Blue, Violet, and deep Green.

The deep and broken tones of the luminous scale become sombre colours, and the light tones of blue and violet become luminous colours.

Orange is the only secondary colour which cannot become cold, because it is composed of two luminous colours, Yellow and Red.

When Yellow predominates in green, we have warm greens; when Blue predominates the greens are cold.

Some hues of Red, Green, and Violet are neither warm nor cold, but neutral.

In colouring maps, geological sections, &c., preference should be given to the luminous colours; and the sombre colours made as thin and pale as possible.

SCALE OF COLOUR.

Scale is the collection of tones of a given colour. There are as many scales of colour as there are hues. Thus we have tones of the Blue scale, tones of the Red scale, tones of the Green scale, &c.

Hues of Blue, designate all the scales, the colour of which still remaining Blue, yet differs from pure Blue; for each hue will comprehend in itself the tones which constitute a scale more or less allied to the Blue scale.

COLOURS OF OBJECTS.

The colours of objects are supposed to be due to a power they possess of absorbing certain portions of the coloured rays that make up a ray of white light, and of reflecting others. The reflected portion being complementary to the portion absorbed; and if added together they would constitute white light.

Thus a red-coloured substance is considered to absorb blue and yellow, and reflect red.

A green-coloured body absorbs red, and reflects blue and yellow. A white substance, then, in conformity with this view, reflects all the rays that constitute white light, while a black substance absorbs them.

Bodies reflect a considerable portion of white light as well as coloured light, according as the surfaces are smooth, glossy, polished, rough, channelled, &c.

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The optical effect of a colour is greatly modified by the condition of the surface of the coloured body; thus, pieces of silk, cotton, linen, woollen, and velvet, although dyed of exactly the same hue and tone of colour, appear to be of quite different colours.

The depth or intensity of colour presented by velvets, and certain flowers, such as heartsease, &c., is due to the surface being channelled, ridged, or furrowed.;

COMPLEMENTARY COLOURS.

As white light is composed of three colours, Blue, Red, and Yellow, the colour that is missing from the compound is termed the Complementary Colour; thus

Blue is the complementary of Orange (Red and Yellow).

Red is the complementary of Green (Blue and Yellow).
Yellow is the complementary of Violet (Blue and Red).

By this it will be seen that the complementary of a primary colour is the secondary composed of the other two primaries, and vice versá; thus:

Orange (red and yellow) is complementary to Blue.
Green (blue and yellow) is complementary to Red.
Violet (red and blue) is complementary to Yellow.

If the Blue is tinged with red, its complementary, Orange, will be
yellower.

If the Blue is tinged with yellow, its complementary, Orange, will be redder.

If the Red is tinged with blue, its complementary, Green, will be yellower.

If the Red is tinged with yellow, its complementary, Green, will be bluer.

If the Yellow is tinged with red, its complementary, Violet, will be bluer.

If the Yellow is tinged with blue, its complementary, Violet, will be redder.

All the complementaries may be easily ascertained by consulting the Chromatic Diagram, Plate VI.

CIRCUMSTANCES WHICH MODIFY A COLOUR.

A given colour, Red, for instance, may experience many modifications, so as to appear very different from what it really is, according to the circumstances under which it is viewed.

It may be modified in its colour :

1o. By being placed in contact with Blue, the red appears yellower. 2°. By being placed in contact with Yellow, it appears bluer.