Regarding the durability of the volatile oils used in the preparation of Cologne water, the following may be said:—
Bergamot oil is quite durable; in well-closed bottles stored in a cool cellar it keeps quite well for 3 to 4 years. Oil of lemons is, however, very sensitive, and has to be especially protected against heat, by which it is readily decomposed and, so to say, turns sour. Freshly-distilled neroli oil should never be used, it acquiring its proper aroma only after being stored for about 2 years; on the other hand, it should not be too old. When 6 to 8 years old, it shows a tendency to rancidity, which can, however, be prevented by mixing it at the proper time with an equal quantity of alcohol of the best quality. Petit-grain oil is apt to spoil when kept for several years, and hence it is not advisable to have too large a supply of it on hand. Besides the French variety of this volatile oil, there has existed for several years past another kind, namely the Paraguay petit-grain oil, which is about one-half cheaper than the French. While some consider both oils as equally good, the French product no doubt deserves the preference. Of lavender oil only the best French oil, especially made in France for the preparation of Eau de Cologne, should be used. The price of the English Mitcham lavender oil, being six times that of the French oil, is simply excessive. Of rosemary oil, an especially fine quality for Cologne water, which can be highly recommended, is also manufactured in France. Of balm oil only the best German product should be taken. The three varieties of volatile oils last mentioned keep for years, especially when kept in hermetically-closed bottles in a cool place protected from the sun.
Rose water and orange-blossom water also need careful treatment, the bottles containing them requiring to be well stoppered and kept in a cool place. These waters being liable to spoil, the supply of them should be renewed from year to year. As regards the compounding of the volatile oils, it is advisable to mix them in a capacious glass flask, add at least an equal weight of alcohol of the best quality, shake thoroughly, let the mixture stand about 14 days, and then in the apparatus incorporate it with the required quantity of alcohol.
When the alcohol and volatile oils are intimately mixed, the mixture is allowed to stand quietly for about 14 days, when solution of the volatile oils will be complete. Now add, with vigorous agitation, the rose water and the orange-blossom water, and let the whole stand quietly to become clear.
Cologne water thus carefully prepared answers all demands. Special attention is here called to the fact that all manipulation by the addition of fixing or conspicuous substances is injudicious. An addition of tincture of musk or civet should particularly be avoided. Nervous people immediately detect such additions, even if present only in very small quantities, and in most cases refuse the Cologne water containing them.
Experience having shown that all alcoholic perfumes develop their proper aroma only after storing for some time, provision must be made to have always a sufficient supply of Cologne water on hand. It is best to keep it in large glass balloons in a cool cellar. Wooden vessels are impracticable on account of their permeability and other evils. Metallic vessels, if used, should be tinned. Vessels defective in this respect, or tinned with tin containing lead, exert an injurious effect upon the aroma of the water. In the latter case, lead is dissolved, even if only in small quantities, and a dirty precipitate injurious to the odor of the Cologne water is formed.
The filtering of the Cologne water is best effected through white filtering paper and a glass funnel; the paper, however, should not have been bleached with chlorine, the odor of the latter being readily perceived and having an injurious effect upon the aroma of the water. Filtering should be avoided as much as possible by carefully decanting off the clear water and filtering the sediment only. Filtering through charcoal, magnesia, or other clarifying agents, should not be made use of for fine perfumes, their odor being injured by all such means.
In the following a selection of receipts for Cologne water is given; it is, however, especially mentioned that only good, pure materials must be used even for the inferior qualities. A receipt for the now fashionable "Maiglöckchen Eau de Cologne" is also given.
Cologne water, quality I.—Bring into a large glass balloon 95 to 96 per cent. alcohol of the best quality 7.9 gallons, lemon oil 14.11 ozs., bergamot oil 15, neroli oil 4.23, French extra lavender oil 1.05 oz., rosemary oil 0.7, best German balm oil 0.42; mix thoroughly, and after 14 days add best orange-blossom water and rose water each 2.64 quarts. Mix again thoroughly, and then let stand until wanted for use.