A pure castile soap should be made from olive oil. This, however, is not always the case, as a number of oils as well as tallow are used to adulterate this oil to cheapen it, and there are even some soaps called castile which contain no olive oil at all. Most of the pure castile soap used in this country is imported, as it is a difficult matter for the American manufacturer to compete with the pure imported castile soap, since both labor and oil itself are so much cheaper in the vicinities of Europe where this oil is produced, that this advantage is more than compensated by the carrying and custom charges by importing the castile soap.
Castile soap may be made either by the full boiled or cold process. There are numerous grades of olive oil, and those used for soap making are denatured to lower the duty charges. Olive oil makes a hard white soap, usually sold in bars, and olive oil foots a green soap, due to the coloring matter contained in this oil.
To make a boiled castile soap, a composition of 10 per cent. Cochin cocoanut oil and 90 per cent. olive oil may be used. To cheapen this, peanut oil (Arachis oil) may entirely replace the olive oil, or about 20 per cent. of corn or soya bean oil may be added. The oils are saponified as usual in making a settled soap and to prevent rancidity the soap is boiled near the finish for some time in the closed state with sufficient excess of alkali to give it a sharp taste, then grained with lye, the lye drawn off, closed with water and then grained with salt. This process is repeated until the desired strength is reached. The last graining should not be too great, and on the last change the soap should not be thinned out, as it will contain too great a quantity of water when slabbed.
In making a cold castile soap the usual method is pursued as already directed under cold made soap. When the soap is taken from the crutcher it is advisable, however, to keep the soap in the frame well covered to assure complete saponification. Some manufacturers use very small frames which are placed into compartments, well insulated to retain heat. Several formulae for cold made castile soaps, follow. It may be noted that some of these contain practically no olive oil.
If any of the soaps containing a high proportion of cocoanut oil are boiled the soap will float. It is therefore necessary to keep the temperature as low as possible.
ESCHWEGER SOAP (BLUE MOTTLED).
Eschweger soap is a colored mottled or marbled soap made to a very slight extent in this country. Inasmuch as it has been introduced to the export trade, it is made for this purpose by some manufacturers. A high percentage of cocoanut oil is usually used together with tallow and grease. About one-third of each is a typical formula. In a soap of this character the fact that cocoanut oil soap takes up a large quantity of water and salts of various kinds and is difficult to salt out is made use of. The tallow and grease are first saponified as usual, then the cocoanut oil is pumped and saponified. When the saponification is nearly completed either silicate or carbonate of soda or common salt are added to make the soap "short" so as to form the mottle. The finishing of a soap of this type can only be gained by practice and it is rather difficult to explain the exact appearance of the kettle at this stage. The surface of the soap should be bright and lustrous with the steam escaping in numerous places in rose-like formation. A sample on the trowel should have a slight sharpness to the tongue and be plastic. When the soap slides from the trowel it should break short. When the soap has reached this stage the desired coloring matter, usually ultramarine, is added to the soap either in the kettle or crutcher and the soap framed. The yield is 200-215 pounds per hundred pounds of stock.
Several modifications of this general method for Eschweger soap are used by adopting the half boiled or cold process.