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.

252 JOURNAL OF THE SOCIETY OF COSMETIC CI-IEtV[ISTS Essential oils known to cause a degree of irritation when in cream but not necessarily acutely: Bitter almond oil 3lace oil Caraway oil Neroli oil Cassia oil Orange sweet oil Cedarwood oil Patchouli oil Celery oil Peppermint oil Cinnamon oil Pimento oil Cloves oil Pine oil Cypress oil Rosemary oil Eucalyptus oil Sage oil Ginger oil Sandalwood oil Lemongrass oil Sassafras oil Limes oil Thyme oil Synthetics known to cause irritation in creams: Acetaldehyde Aldehyde C.8-C.20 Aubepine Benzylidene acetone Benzyl alcohol Borneol Cuminic aldehyde Diethyl phthalate Dimethyl benzyl carbinol Ethyl acetate Ethyl alcohol Eugenol Heliotropine Hydroxycitronellal Bromstyrol Butyl alcohol Carvacrol Cinnamic aldehyde Citral Citronellal Iso-propyl alcohol Menthol Methyl cinnamate Methyl heptin carbonate Methyl phenylacetaldehyde Musk xylol Phenylacetaldehyde Thymol Essential oils known to cause discoloration in creams: Bay oil N•roli oil Birch tar oil Sweet orange oil Cassia oil Patchouli oil Cedar oil Pimento oil Cinnamon oil Sage oil Cloves oil Vetivert oil Lavender oil It is safe to presume that most of the absolute oils and gum resins will cause discoloration in creams.