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

472 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS keep the water content to a minimum. Certain film formers, such as Devlex A.515, may require the addition of methylene chloride or 1,1,1- trichloroethane to the alcohol. Methylene chloride may also be used to prevent precipitation of the film former, and other ingredients, when chilled concentrates are used for cold-filling. Methylene chloride may cause damage to painted, lacquered or plastic surfaces if the sprayed lacquer impinges upon them. For water-based lacquers, IndustriM Methylated Spirits diluted with de-ionized water is used. Film Formers The ideal hair lacquer should provide a set, without tackiness, which will be maintained under varying conditions of humidity. It should impart gloss and a good "feel" to the hair, should have good adhesion and not flake off. The film should be sufficiently water-soluble to permit re-comb- ing, and also removal by washing. No film former will meet these require- ments fully and although some of the more recently introduced resins show improvements in some respects over the old established products, it is still necessary to incorporate modifying agents into the fornmlation to minimise or eliminate undesirable properties. A wide variety of film formers have been tested, but most have proved unsuitable in some respect. Instability of colour, odour, corrosion problems, skin irritation and poor solubility in suitable solvents, are some of the causes for rejection. The development of new film formers for hair lacquers may now be retarded, as the screening for toxicity of inhaled spray particles will have to be carried out over long periods. For the conventional hair lacquer the film former should be soluble in anhydrous ethyl alcohol (Industrial Methylated Spirits 74 o.p. is used) and in the final alcohol/propellant system. For water-based hair lacquers the film former must be soluble in 50-60% ethyl alcohol. It has been men- tioned above that auxiliary solvents, such as methylene chloride may be used where the solubility in alcohol, particularly at low temperatures, is inadequate. The concentration of film former varies with the type and the particular purpose for which the hair lacquer is marketed, but it is usually within the range of 2.5-10% in the concentrate. There is an extensive literature dealing with the chemical and physical properties of film formers used in hair lacquers, which also gives details of large numbers of formulations. It is, therefore, only necessary to sum- marize these details hereunder. Shellac The first film former to be used in pressurized hair lacquers was shellac which, although it does not fulfil many of the requirements quoted above,