The paints made with these substances are called by special names, and often have peculiar qualities which adapt them for use under particular circumstances.
It would be almost impossible to give a complete list of all these special paints, but it will be useful to mention a few of the most prominent with their characteristics.
Inodorous Paint1 is mixed without any turpentine, the evaporation of which in ordinary paints causes a strong unpleasant smell, which in some people produces headache, and even more injurious effects.
In this paint the ordinary white lead, or zinc white ground in oil, "instead of being thinned with oil and turpentine, is mixed with methylated spirit in which shellac has been dissolved, together with a small quantity of linseed and castor oil."
"This methylated spirit evaporates very rapidly, leaving behind the shellac, which acts the part of the film of varnish left by the oil and turpentine in the ordinary method of painting, protecting the wood or stone, and at the same time attaching the pigment to the painted surface."
This paint dries very rapidly. The second coat can be applied an hour after the first, and three-coat work can be finished in one day. The rapid drying makes it difficult to paint a large, uninterrupted surface, without showing marks where one portion dried before the next was commenced.
For interior work in occupied buildings this paint has very great advantages; also where rapidity in execution is required, but it is not so durable as paint mixed in oil and turps.
"In oak graining it is desirable, perhaps better, that the varnishing coat should be put on as usual; but in this case the odour arising from two coats of paint work is at all events avoided, and the whole is finished in a day, instead of lasting over two or three days."1
Freeman's "Non-poisonous" White Lead "is prepared by grinding under considerable pressure a precipitated sulphate of lead with 25 per cent of zinc oxide, whereby the density of the mixture is greatly increased. This preparation possesses the advantage of a very simple and unobjectionable method of manufacture and of keeping its colour better than ordinary white lead when employed in situations exposed to air containing sulphur compounds, such as in railway tunnels. It is equal to the ordinary white lead in point of colour, and is reported to be so as regards 'body' and 'durability,' but this last point can only be decided after the lapse of sufficient time." 2
Charlton "White is a mixture of sulphate of zinc with sulphate of baryta or strontia. It is more pulverulent than zinc white, and more opaque. Requires more oil than white lead, less than zinc white. Tested for body by saturation with blue, it shows itself to be 60 per cent stronger than zinc oxide and 30 per cent stronger than genuine white lead. It must be used with lead, less direct, and is not affected by sulphurous vapours. In outdoor work it must be "bound" by varnish, and in all cases it is perfectly harmless to makers or users.
Charlton Enamels are preparations of Charlton white, and gums, which dry with a smooth hard surface and do not crack or blister.
Duresco is a preparation of Charlton white worked up by a process which is a secret. It dries out perfectly "flatt," is quite solid, washable, and non-poisonous, is much less expensive than oil paints, and more easily applied; all this makes it peculiarly valuable to internal wall decoration.
A patent White Sulphide of Zinc Paint is manufactured at Liverpool by the Sanitary Paint Co., which consists of a mixture of sulphate of zinc and sulphate of baryta. . . . This paint when not properly manufactured has sometimes been found to become discoloured under the influence of strong sunlight, the dark tinge which it assumes passing off again after a few hours." 2
Griffith's Patent White Paint is a form of zinc paint which has recently been introduced. Its basis, oxy-sulphide of zinc (see p. 409), is said to be cheaper than white lead. It has 25 per cent more covering power for the same weight, is not poisonous, is more stable, is of a brilliant white colour, dense, and opaque; does not blister or yield to heat or gas, is not discoloured by sulphuretted hydrogen, is neutral towards iron, and will mix with colours which white lead destroys.
Albarine is a white enamel which is found to be very superior as regards hardness, enamel-like appearance, whiteness, and easy application; one gallon will cover on an average 50 yards.
2 Dent's Cantor Lectures.