470 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The conventional pressurized hair lacquer consists basically of an "anhydrous" alcoholic solution of a fihn former, together with a chloro- fluorohydrocarbon propellant system, whereas the so-called water-based product, now appearing in significant numbers, employs an aqueous alcohol as the solvent and a hydrocarbon propellant system. In both types, other ingredients such as auxihary solvents, plasticizers, perfumes, corrosion inhibitors, "conditioning" agents and spirit denaturants may be included. The composition of the "concentrate", i.e. the solution of film former and other ingredients, the type of propellant system, the ratio of propellant to concentrate, and the type of valve used, are the four critical factors which together determine the performance of the complete hair lacquer. The hair lacquer is a surface coating product and whilst some formulation and laboratory evaluation problems are similar to those encountered with paints, there is one significant difference--the substrate to which the hair lacquer is applied. Not only do the natural characteristics of hair vary considerably from individual to individual, but the hairs may also be damaged or modified by bleaching, permanent waving, or by the use of rinses. The hair shafts vary in thickness and have an irregular surface "lubricated" with sebum, which is a varying mixture of fats, fatty acids, hydrocarbons, sterols, inorganic and organic salts. Apart from these varying properties of the substrate, none of which would commend themselves to a paint technologist, there is also the problem created by the ultimate user. The lacquer will be sprayed from varying distances despite explicit instructions on the dispenser, and, similarly, the quantity applied will vary sharply. It is not surprising, therefore, that laboratory evaluation of hair lacquers must be supplemented by user trials despite their limitations. LAgORATORY EVALUATION There are a number of factors governing the efficacy of hair lacquer which can be evaluated in the laboratory. These procedures can be used for quality control purposes, and for the initial screening and comparison of new formulations. Tests on locks of hair give valuable information, particularly regarding ease of combing and the tendency to flaking or stripping of the lacquer film. The primary purpose of a hair lacquer is to hold the hair in the desired position, which is achieved by the stiffening effect of the film former which will be modified by the presence of other ingredients such as plasticizers, perfumes, lanolin derivatives, etc., and also by the humidity of the atmos- phere. The stiffness or holding properties of the hair lacquer may be checked by several methods. Switches of hair which have been set into curls by water, dried and then sprayed, can be suspended in a controlled

HAIR LACQUER SYSTEMS AND THEIR EVALUATION 471 humidity chamber, and the degree of return to the original shape measured. The Shirley Cloth Flexometer •'2, which measures the degree to which strips of material, secured at one end, bend under their own or added weights, may be used for comparing the degree of stiffness imparted by various lacquers. Strips of filter paper (Whatman No. 41) or other suitable materials are impregnated with standard amounts of lacquer, dried and tested. The same procedure can be carried out at varying levels of humidity. The deposition of hair lacquer on "living" hair is somewhat uneven, depending upon a variety of factors such as distance and duration of spraying, and degree of penetration, but, nevertheless, these methods of comparing stiffness provide useful data. A further important requirement is that the lacquer shall impart gloss or sheen to the hair. The gloss meters and reflectance spectrophotometers used in the paint industry are of little value for measuring the gloss of a lacquer film on hair, because of the variations in colour, texture and surface characteristics. Tests for gloss must, therefore, be conducted visually either on switches of hair or on living subjects. The spraying of hair lacquer on to glass plates will, however, reveal basic faults in the formulation giving cloudy or hazy films. Many of the film formers used in hair lacquers are hygroscopic and since they are plasticized by water, the lacquer film will not only soften but may exhibit the highly undesirable property of tackiness. A simple method of measuring tackiness is to determine the weight which has to be applied to a piece of aluminium foil to make it adhere to a lacquer film on a glass plate, so that on inverting the plate, it will not fall off a. The standard laboratory procedures are used for determining particle size, spray pattern, discharge rates and pressures. FORMULATION OF CONCENTRATE Solvents Ethyl alcohol (Industrial Methylated Spirits 74 o.p.) is almost invariably used as the basic solvent for hair lacquers, although isopropyl alcohol, with its less severe corrosive properties, lower cost and freedom from Customs and Excise regulations in respect of denaturants, is used to a limited extent. Its odour, however, militates against its use except for products where cost is the prime consideration. The Customs and Excise Authorities require the addition of denaturants to the product, except in the case of shellac- based hair lacquers containing not less than 6 oz of shellac per Imperial gallon (i.e. concentrate excluding propellants). One or more of the following may be stipulated: Solution of quassin, diethyl phthalate, Cetrimide, sucrose octa-acetate, Bitrex solution. For conventional hair lacquers, the manu- facturing and loading processes must be carried out with stringent care to