THE ingredients of ordinary paints are white lead or zinc white; raw or boiled linseed oil, or both; turpentine; driers; and, in the case of coloured paints, pigment.
The first is the base, or chief protective material; the oil enables the base to be distributed by the brush, and when it dries, that is, hardens by oxidization, also helps to protect the work. Turpentine is used to thin the paint, but, being volatile, it does not remain in it permanently. Driors are added to hasten the hardening of the oil.
The larger the proportion of turpentine to oil, the flatter will the paint dry; and, conversely, a preponderance of oil tends to produce a glossy surface. Turpentine is commonly omitted from a first coat on new woodwork, called the priming coat, as the oil is quickly absorbed by the wood; and from the final coat for outside work exposed to the weather; as in this case thinning is done better with oil entirely, to obtain the maximum of protection.
The amateur may well be content to try paints ready mixed for at least the final coats. But he should avoid cheap paints. The extra cost of the products of the best firms justifies itself many times over.
It is easy onough to mix paints for under coatings, if the worker provides himself with supplies of oil, turps, driers, white lead or zinc oxide paste, and pigments ground up in oil. And this course has the advantage of enabling the paint to be mixed differently for the various coats, which, as already hinted, should be somewhat differently constituted.
MIXING AND STRAINING IF, when a tin of paint is opened, there is a film of hardened oil on the surface, this should be cut away from the tin all round the edge with a knife and be carefully removed as a whole. The paint is then mixed thoroughly with a flat stick, worked into the angles of the tin until no signs of deposit remain.
It is advisable to strain all paint intended for indoor use, as it may contain small lumps and fragments of skin which, if left in, would disfigure the surface. A strainer is quickly made by cutting the bottom off a tin canister, beating the edgo out a little all round and tying on to it a square of the canvas called scrim, obtainable from most linendrapera.
The strainer is stood on two stioks laid across the paint pot, and the requisite amount of paint poured into it. Scraping the canvas insido with a stick will assist the paint to run through. The canvas should be renewed every day. ,j PREPARING NEW WOODWORK THE wood is first sandpapered and – dusted. Then any knots are coated with patent knotting to prevent resin pozing out. The next step is to paint the wood with a priming coat – a mixture Of white lead (or zinc white), oil, a very little, if any, turpentine, a little driers, and enough red-lead to produce a salmon-pink colour. The red lead makes the paint dry quickly and very hard; the oil, by entering the wood, prevents it absorbing oil from the next coating.
All holes, dents, and cracks are now filled in with putty, smoothed down with a putty knife. When the putty is hard, the surface is sandpapered smooth, and everything is then ready for the colour coats.
THE first colour coat (for Inside wood- work), which may be called coat A, will be composed of a pint of raw oil, half a pint of turps, and two ounces of driers to every four pounds of white lead, and pigment. If the final coat is to be, say, green or brown, the paint may be darkened to a grey by the addition of black. It will then conceal the priming coat better.
Coat A is applied with strokes in all directions, finishing with strokes in the direction of the grain only. When dry, the surface is rubbed with fine sandpaper along the grain.
The second colour coat, B, must be mixed to suit the nature of the final coat 0. If C is to be flat – non-glossy – B should be weak in turps but rich in oil. Conversely, if a glossy or enamel C is intended, B should contain little oil, but plenty of turps. Pigment as before, but of a somewhat differont shade, as this will make it easy to see if any parts are missed by the brush. The paint is rubbed down.
A flat C coat should contain little oil, if any; a glossy coat, little turpentine. This coat is pigmented to the final colour desired, and is not rubbed down. A little varnish added to C will make it dry very hard.