Among the ancient Greeks, Romans, and Germans various ointments were in use for the care of the hair. In Rome there was even, as we have stated in an earlier part of the book, a special guild of ointment-makers or unguentarii. They employed a process for making their ointments fragrant which resembles that of maceration in present use.
The so-called pomades (from pomum, apple) were prepared by sticking a fine apple full of spices and placing it for a long time in liquid fat which absorbed the odor of the spices.
In the present state of chemical science, the basis of every pomade or hair oil is formed by some fat perfumed with aromatic substances and at times colored. The fats generally used are lard, beef marrow, tallow, bears’ grease, olive or almond oil; some of the firmer fats receive an addition of a certain amount of paraffin, spermaceti, or wax, in order to give the pomade greater consistence. As in the manufacture of all the finer articles, it is essential that whatever fat is employed should be perfectly pure; only fat which is absolutely neutral, i.e., free from acid, can be used, and any sample with but a trace of rancidity (containing free fatty acids) should be rejected on account of the penetrating odor peculiar to several of these acids.
Manufacturers who aim at the production of fine goods spare neither trouble nor expense in order to obtain perfectly pure fats.
Fats are purified for the purposes of the perfumer in the following manner:
The fat is melted in a bright iron pot or enamelled vessel with three times the quantity of water containing in solution about one per cent (of the weight of the fat) of alum and one per cent of table salt. Fat and water are well stirred with a broad flat ladle or some mechanical arrangement within the boiler. After the mass has remained at rest for some time, the curdled solid matters are skimmed from the surface. The time required for this operation can be much shortened by the use of a pump which raises the fat and water from the boiler and returns them in a fine spray.
When fats with some degree of rancidity are to be made suitable for the purposes of the perfumer, 0.5% of caustic soda lye is added to the water instead of the alum.
After this treatment is completed, the fat must be washed in order to free it from the substances with which it was purified. Formerly this washing was done in a manner resembling the grinding of oil colors. The fat was placed on a level stone plate and kneaded with a muller with flat base under a continual stream of water flowing from above, until the fat was clean. This expensive hand labor is now performed by machines, the fat being treated with water in vertical mills.
No matter how carefully a fat was purified, it may happen that the pomades made from it, if kept long in stock, may subsequently become rancid—a circumstance which may destroy the reputation of a factory. Fortunately we know two substances which materially counteract the tendency of fats to become rancid: salicylic acid and benzoin. Either of these substances is added to many perfumery articles, especially pomades, in order to prevent rancidity; an admixture of from one-one-thousandth to five-one-thousandths parts of solid salicylic acid suffices, according to our experiments, for the purpose; of benzoin we need about three-fourths of an ounce for every quart of fat; the resin is only partly soluble in fat, but imparts to it its vanilla-like odor. For the finest pomades sublimed benzoic acid is used, in the proportion of about 150 to 240 grains to the quart of fat.