All about Paint
The materials used by the painter and decorator in the exercise of his craft are so numerous that to do full justice to them would require far more space than is at our disposal.
It is not claimed that the list which follows is in any way complete; it is mainly, though not exclusively, concerned with paint and its constituents, since the materials used in decorative processes other than painting will be dealt with in their relevant chapters.
Paint is a generic term for a large number of different types of material, ranging from colour wash to the finest enamel.
To the decorator, however, the word invariably refers to an oil or gloss paint, of which there are four components - the pigment, the vehicle or medium, the thinner, and the drying agent.
1. The pigment provides body, opacity or obscuring power, and colour.
Pigments are derived from various metals, earths, and other sources, and the degree of fineness to which they can be ground is a highly important consideration.
They are usually supplied to the painter in paste form, ground in linseed oil, turpentine, or gold size, although they are also available in dry form. In most paints, the bulk of the pigment is a basic white, with or without the addition of coloured pigments or stainers.
2. The vehicle or medium is a drying oil, such as linseed oil, a varnish, or a mixture of both. Its function is to enable the particles of pigment to be applied to a surface in a uniform coating and to remain attached to that surface. Linseed oil dries mainly by oxidation, that is, by absorbing oxygen from the air; changing, in doing so, from a fluid into a tough, leathery substance known as linoxyn.
The process, it should be noted, is a gradual one which continues long after the paint is dry to the touch, and brings about an alteration in the structure of the oil as the result of which
the linoxyn is not soluble in turpentine.
The proportion of vehicle to pigment governs, to a great extent, the degree of gloss which the paint film possesses, as well as the durability of the coating.
3. The thinner is a term sometimes applied to the liquid portion of the paint as a whole, but more generally to the volatile liquid which is added to the paint to make it more fluid and thus more easily put on.
For oil paints, the thinner traditionally employed is turpentine, though mineral spirit (known as "white spirit" or "turpentine substitute(sub-turps)") is widely used. especially by paint manufacturers, since it is considerably cheaper:
provided it is of good quality, it serves equally well for the purpose as pure turpentine.
4. The drying agent, or drier, is a substance available in paste, liquid, or powder form, which is added to the paint to accelerate oxidation of the film. Driers are essential ingredients since without them the paint would take too long to dry for practical purposes, but the more sparingly they can be used the better, since they tend to shorten the life of the film.