COSMETIC KNOWLEDGE THROUGH INSTRUMENTAL TECHNIQUES 127 principle occurred. The mechanical phase of hair waving was supplanted by the chemical phase (1). Manual dexterity with the hot curling tongs was replaced by mental dexterity in the cold light of scientific research. This led to the seemingly paradoxical use of mercaptans in cosmetics (2), a development which appeared to fly in the face of the entire experience of the cosmetic industry. These mercaptans have been used in waving lotions and depilatories in a powerful demonstration of the superiority of the scientific method over curling iron, razor blade, tweezers and depilating wax. The third phase, which we have entered but comparatively recently, can be called the "era of physico-chemical measurement," a development which should make Lord Kelvin rest more easily. We have seen the gradual development of measurement techniques to aid cosmetic research in control work and in the evolution of new processes. We have pH, colori- metric and viscosity measurements on the one hand, and empirical measure- ments for detergency, foam stability and emulsion stability on the other. Probably the uses in analysis have had most emphasis, but the new instru- mental techniques are also very valuable for determining the effects of cosmetics upon hair, skin and teeth. They show the functioning of proc- esses, the absence of undesirable effects, the creation of desirable effects and the way to even better cosmetic products. It is important these days to show that cosmetic products not only cover blemishes and change the color of the skin and hair, but also that they pro- duce soft and smooth skin, better combing, increased luster and improved hair manageability. Unfortunately, methods for measuring these proper- ties are not always at hand, and the problem of measurement arises. How should the measurement be made ? By human senses or by machine ? On fundamental properties or on some empirical basis ? Before attempting to answer these questions, certain generalities, often overlooked, about instruments should be considered: (1) Instruments are developed for the convenience of man. They are designed to give him information more conveniently and more accurately than he could get the same results by hand. (2) An instrument is a measuring device which can give information on three levels: (a) bulk properties, (b) molecular properties and (c) atomic properties. Most instruments can be classified accordingly. (3) An instrument is designed to fill a gap in knowledge. The instru- ment for a given application is chosen according to the type of knowledge that is needed to solve a given problem. (4) The area where the knowledge is needed governs the design of the instrument, rather than of the instrument governing the field of applica- tion. (5) The results given by an instrument will be meaningful only in re-

128 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS gard to the conditions of the measurement employed. When different in- strumental approaches are used to measure a certain property or effect of a substance, all the results obtained may be equally valid but only some of these results will be useful. Useful results are often the hardest or most expensive to obtain. This is particularly true in cosmetics where so many subjective terms are current. Ultimately, a subjective term has to be measured subjectively, but the instrument can play a valuable part if some correlation can be established between physical measurement and subjective response to a cosmetic prod- uct. Cosmetic research at Evans Research and Development Corpora- tion has been greatly aided by a variety of techniques, some common and some less well known. PAPER CHROMATOGRAPHY Paper chromatography within a space of ten years has grown from nothing to one of the most important methods of analysis in the whole ASCENDING DESCENDING 1 2 3 1 2 SF SF SF OP q¾ OP SL SF SF SL Figure 1.--Paper chromatogram of brown hair dye. SL = starting line, SF = solvent front, R = red, B = blue, P = pink, G-Y = green-yellow, Y = yellow, 1 = 4:1:5 n-butanol- acetic acid-water, 2 = 100:20:44:1 n-butanol-ethanol-water-ammonium hydroxide and 3 = 4:1 phenol-water.