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Water-Colour Painting

Water-colour Painting. - The usual binding material in this method is gum; glycerin and honey are also employed to some extent. Raw honey should never be used, but only one of the sugars it contains, known to chemists as laevulose. Great care must be taken not to introduce any unnecessary excess of either glycerin or laevulose, as these materials attract moisture from the air, and we know that moisture is one of the most potent agents in causing injury to works in water-colour. Glycerin and laevulose are, however, useful, when employed in moderation, for preserving the pigments in working condition, and in counteracting the tendency of gum to crack. The media used in water-colour painting, consisting wholly of aqueous solutions, afford very slight protection to the pigments used. In the presence of the moisture of the ground (paper often contains naturally 10 percent of water) and of the air, water-colour pigments have abundant opportunities, not only of acting upon one another, wherever from their chemical constitution such action is possible, but also of being acted upon by external agents.

Thus it comes to pass that several pigments (vermilion, for instance, and emerald green) useful in oil-painting cannot be safely used as water-colours. Again, there are a few pigments (such as strontia yellow) which are soluble in water, and which consequently may gradually sink into the paper, and so partially disappear from the surface.

Assuming the paper-ground to be of linen-pulp, and free from 'filling,' from bleaching substances, from anti-chlors, and from fragments of iron, it will still contain about 5 percent of size. When in preparation for painting it is moistened with water, this size swells, and on the subsequent application of washes of pigments, enters partially into mechanical union with them, so that the various coloured materials applied to the surface become associated with the size rather than with the paper-fibres. One paint, Indian ink, itself contains size, and for this reason when washes of it are laid upon paper previously damped, their incorporation with the size of the latter is so intimate that their removal is impracticable. The size in a water-colour drawing becomes in time partly coagulated and insoluble; the gum merely dries. Instances are known where the size has in some degree ultimately perished.

Last Update: 2011-01-23