The part played by chilling in the production of a high-class crystal-clear perfume is not always appreciated to the full among perfumery manufacturers in this country (England). Briefly, the technique of manufacture is as follows:
In the first place, there are two chief methods of compounding. One is based on the idea of the alcohol as a separate unit, and consists of pre-fixing (or deodorising) the spirit, prior to dissolving in it the finished compound. This procedure, which is known also as the English method, is described admirably in detail in Poucher's Perfumes, Cosmetics and Soaps, Volume II. There is, therefore, no need to enlarge upon it here. The alternative, or French method, consists of building up the perfume from 10 percent alcholic tinctures of the various raw materials.
The latter method is usually to be preferred, so far as the quality of the finished perfume is concerned, but it has the greatest disadvantage attaching to it of causing a much larger bulk of raw materials to be left about the premises, instead of the more convenient procedure of keeping the solvent and other constituents apart, until the final mixing and maturation.
When the English method is employed, the proportion of raw materials (i.e., essential oils, synthetics, natural absolutes, fixatives, etc.) should not exceed some 10 to 15 per cent of the quantity of solvent used. With the alternative method, a mixture is simply made of the various alcohol tinctures.
The possible addition of water, which in the cheaper perfumes amounts sometimes to as much as 20 per cent, lends itself very readily to the precipitation of the less soluble bodies. In any case, filtration is essential, if it is desired, to obtain a really crystal-clear product.
The mode of filtration shows little variation. Filtering may be effected either through filter paper, or through one of the special mineral products that are now being offered. The latter are used in conjunction with such improved pieces of apparatus as the Seitz filter--this being a popular type on the Continent that may be obtained for use either with or without pressure.
After filtration has been properly carried out, a perfectly clear and brilliant solution should be obtained, but unless the solution has been chilled prior to filtration, there is still most likely to be a progressive precipitation over a period of months, particularly during cold weather. This is especially the case with certain synthetics, and also with perfume concretes that still contain traces of wax and other impurities. The latter are frequently soluble in essential oils and alcohol at normal temperatures, but are precipitated as soon as the temperature is lowered.
An old trick of the trade, used in conjunction with the English method of compounding, is to dissolve the concentrate in three-quarters of the alcohol, plus any water that has to be incorporated. The perfume is then chilled, filtered, and subsequently the other quarter part of the alcohol is added. This, as one would expect, is a very effective guard against further precipitation.
It should be particularly emphasized that chilling is an essential part of perfumery production, and a refrigerator adapted for the purpose should be installed in every factory.