Water-Colour Painting

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.