Good paint of this description should be made of pure white lead. If it is to be untinted, care must be taken to exclude any substance which will detract from the brightness of the white, and it must be kept in closed vessels, or the action of the air will give it a brown shade.
Uses, Advantages, and Disadvantages. - White lead paint itself, and also as a basis for coloured paints, is one of the commonest and best protecting coverings that can be applied to surfaces of wood. Where it is exposed, however, to the fumes of sulphur acids, such as are evolved from decaying animal matter, in laboratories, and in some manufacturing towns, it soon becomes darkened by the formation of black sulphide of lead. It has also the disadvantage of producing numbness and painters' colic in those who use it.
Coloured Lead Paints are made by adding to a basis of white lead paint certain stainers or colouring pigments described at p. 413.
A list of some of the pigments used to produce different tints is given at page 422.
It is better to ascertain the proportion required by experimenting at first upon a small sample.
Where the colour is very deep, the amount of pigment becomes very large in proportion to the white lead; and in some cases, as in very common black paint, the white lead is omitted altogether, to the great detriment of the protecting qualities of the paint.
The colouring pigments, if any, are then added, and the paint is brought to the consistency of cream by adding more oil and turps.
It is then cleared by passing it through a canvas or tin strainer.
When about to be used, the paint is thinned to the consistency necessary to enable it to work freely, by adding more oil and turps, called thinnings, and the driers are also added.
If the paint is too thick, it will be difficult to work, and will make an uneven surface. If too thin, it will not have body enough, and more coats will be required.
As the paint becomes thicker during use, or when put upon one side for a time, it will require further thinning, and perhaps repeated straining to clear it from skin and dirt.
Lead paint produces most injurious effects upon those who use it.
Entering the pores of the skin, it is absorbed by the system, and leads to numbness and a kind of paralysis. It also produces a complaint known as "painters' colic."