Among those that interest paint manufacturers mostly should be classed soya bean oil, corn oil, cottonseed oil, castor oil, rosin oil, pine oil, tar oil, seal oil and mineral (or paraffine) paint oil.
Soya Bean Oil averages in specific gravity .926 and whereas raw linseed oil dries to a firm film in six days bean oil requires fully ten days and then the film will not be as firm. When linseed oil was extraordinarily high priced several years since there was quite a great demand for bean oil, and it was quite a task for paint makers to discover methods to make their products dry in the ordinary way. The usual practice was to use equal portions of soya bean oil and boiled linseed oil, or when this would not work out well in some paints the bean oil portion was increased and also the driers. While paints made on such formulas could not pass chemical inspection when linseed oil was specified, and therefore could not contain admixture of bean oil, observations have proved that such paints did wear very well, while paints doped with so-called paint oils or other nostrums went to pieces.
Corn or Maize Oil has been in use in paints for many years, but is made use of only when linseed oil is much higher in price. This oil has very little, if any, drying properties, and will harden to a brittle, rather mealy film in from twenty to thirty days. When used alone for grinding pigments the paste comes from the mill like a cornmeal mush, and emits a similar odor, especially when the mill becomes heated, as it usually will, the oil not being a good lubricant. It is now chiefly used in putty making, mixed with paint and putty oil in varying proportions.
Cottonseed Oil has no drying properties, but is a good lubricant, and previous to its rise in price, when it came to be used as a cooking and table oil, it was used to adulterate linseed oil. Under certain conditions, such as to keep paint or putty from hardening on long standing, it is still added in small percentages. There can be no mistake about the oil. It is of the same lardlike odor as cottolene.
Castor Oil (a semi-drying oil) in color or paint is used only with pigments that are afterward thinned with guncotton lacquers to produce an elastic yet firm film for metal packages and other special purposes too numerous to mention.
Rosin Oils are not only used in printing-ink making, but were largely employed in making paint for rough surfaces, though since their price has advanced to twice, even three times their former cost, they have been replaced by mineral paint oils to a great extent in paint. Rosin oils are practically non-drying, and while they harden in time will soften again under the influence of sun heat and make the paint film part, or alligator.
Pine Oil and Tar Oil are products from the distillation of wood spirit and of rosin, and are used in the manufacture of marine paints, especially paints for ships' bottoms. These oils are semi-drying and water resisting to a degree.
Seal Oil, the bleached or white variety, is also semi-drying, and on account of its lubricating character is used by the makers of enamels in small percentage, two in one hundred by volume for free flowing under the brush.
Mineral Paint or Paint and Putty Oil, so called among the trade, is refined petroleum or neutral oil, so named because debloomed. These oils cannot be used without being mixed in certain percentages with boiled linseed oil, as they lack binder and are apt to wash off the surface in case of driving rains. Even when used in large portions in a liquid paint for rough surfaces such paints have been known to wash off when they were supposed to have dried hard a month or two before. Petroleum products of this class will sweat, causing softening of the film and consequent damage by water.
Cheap paint for rough lumber or other rough surface can be made by grinding the base in linseed oil (usually boiled) thinning with a mixture of thirty-five gallons gloss oil (rosin and benzine mixture), ten gallons raw linseed oil and five gallons liquid dryer. Or if it must be still cheaper make a thinner of thirty gallons gloss oil, fifteen gallons debloomed neutral paraffine oil and five gallons lead and manganese drier. In any case, however, grind the pigment to be used as the base for the paint in linseed oil.