250 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS plexes can be adopted for a particular line if it is to be correctly perfumed, and it is much better for a perfumer to design a perfume than to endearour to modify an existing one just to retain a similar tonality throughout a range of products. The reason for the co-operation between the cosmetic chemist and the perfumer is evident when a cosmetic preparation shows deterioration. The formulation must be examined to determine whether the perfume used is the cause or whether the preparation would break down irrespective of the added perfume. In such cases (and we do come across them), the whole formulation of the cosmetic preparation must be adjusted to accept a perfume, and the perfume must be adjusted where it is proven that a particu- lar component is the aggressor. It may be that the perfume is being added at the wrong stage of manufacture, and this should be taken care of. This is a little more important than is at first envisaged, and the perfume in a preparation might well appear much better if it had been added at the correct stage in the manufacture this again is where the chemist and perfumer should work together to obtain the best results. It may also be possible that a reduction in perfume content could be effected by this means and thus effect a saving in manufacturing costs. We often have complaints of discoloration, a phenomenon which shows mostly after an ageing period. This can be due to many causes, and a close examination of the components of the cosmetic pack might possibly reveal the cause. Insolubility of perfume in a liquid preparation is another trouble- some problem which must be overcome, and it is only when knowing the formulation that the perfumer can take the necessary precautions to eliminate the insoluble matehals in this compound. Whilst the cosmetic chemist might not be aware of solubilities of perfumery matehals, the perfumer would know the solubility of the ingredients of his creation. The advent of aerosol products has brought tremendous perfumery problems. The many factors that have to be controlled to ensure that the perfume does not deteriorate include the solubility of the perfume in an aerosol formulation, the stability, and the possibility of aromatic bodies being irritants. This method of dispensing a perfume and the results obtained are so completely different from all previous methods and results that the perfumer has had to revise the techniques employed in creating a perfume for use in this medium. The whole of the complex--the top notes, the heart, and the residual notes--are instantaneously atomised into the atmosphere, and the result is completely different from that obtained when using the conventional air spray. This difference is great, and to obtain similar results by the two spray methods two different perfumes would have to be prepared. Because there are so many factors governing the creation of a perfume for aerosol dispensing prior to being finalised it must be subiected to a shelf-test in a loaded aerosol for a period of not less than six months to

THE ART OF THE PERFUMER 251 ensure complete satisfaction. The result from an accelerated test is con- clusive only if it is adverse. This means that an aerosol can develop deteriora- tion after an accelerated test is carried out, and specific cases have indeed been experienced. The perfume for an aerosol must be governed by the type of product being loaded, as the ingredients can affect the perfume or be affected by the perfume. It is imperative that there are no precipitates to cause deposits or clogging of the valve, and care should be taken that all insoluble matter is removed from any formulation, preferably before compounding a perfume. Having created and developed a perfume, this must be tested in suitable aerosol formulations and then the products must be shelf-tested. Perfumery being a slow business, ageing or maturing takes six months. It is advisable to smell and examine the aerosol during this period and all the various changes in character, if any, should be noted. Evaluating the odour of an aerosol might be difficult for the inexperienced, but I suggest that the aerosol is sprayed lightly on to a filter paper and that this sprayed filter paper is examined, together with the usual tests of spraying the product into the atmosphere or on to the skin or on a garment, or on to anything which will give a correct appreciation of the perfume. Whilst it will be noticed that in some instances there is irritation of the skin and mucous membrane, this is not necessarily caused by perfume ingredients, but sometimes by the aerosol spray itself, especially if one walks into a spray immediately after it has left the spray head. The fact that the whole perfume complex is to be smelled in an instant is areason for modifying perfume compounds for aerosols, together, of course, with the many other factors relating to aerosols generally. All these factors have to be taken into consideration by the perfumer when he attempts to create a perfume, whether it is intended for a handker- chief perfume or a perfume for a cosmetic preparation, and it is very important that the perfume has an •esthetic appeal, that it has tenacity, that it is stable and that its ingredients are compatible. After complying with the foregoing it must be compatible and stable in the preparation being perfumed. It has frequently been mentioned that many materials have irritating effects on the skin and that many tend to discolour a toilet product. It might therefore serve a useful purpose to give some indication of these matehals. The intensity of the bad effects obviously depends upon the dosage and, although many products are mentioned as possible irritants or possible colorants, it will be noticed that small percentages of them are often incorporated in formulations. Sometimes the adverse quality is unnoticed at a low dosage. Where there is a tendency to discolour, the end-product is often tinted or coloured to impart an attractive appearance and/or to cover a blemish. So with the skill that comes from experience the perfumer will discriminately use many materials which are mentioned as possible sources of trouble.