NAIL ENAMEL TECHNOLOGY 35 The total solids in an enamel is usually determined by drying weighed amounts in a laboratory oven and calculating differences in weights. Film characteristics are usually evaluated primarily on fingernails compared to a standard. A clean glass panel and a Bird Film Applicator (Bird & Son, Inc., East Walpole, MA 02032) may be used to apply a standard amount of batch and lab. master to determine drying time, film clarity, gloss, and comparative hardness and adhesion. Hardness and adhesion may be compared by scraping dry films which have been set aside for 4-5 hr with a slightly curved knife. Experience with this test method will yield more dependable information than involved procedures utilizing complicated equipment. Settling tests, comparing a known standard and batch which have been subjected to elevated temperatures of 40 ø C and 50 ø C for a given length of time, is used to measure relative settling rates. Color should match in the bottle and on the fingernail. To compare colors on the nails, one applies the master sample on the middle finger and batch sample on the immediate fingers to the right and left. After drying, color should match in normal daylight or under a Macbeth Daylight lamp (The Macbeth Corporation, Box 950, Newburgh, N Y 12550). An alternate method is to compare colors on two thumb nails. In order to ensure that the color strength of the master sample matches the batch, one applies a three mil .003-in-thick) wet film on a black and white Morest Chart (The Morest Company, Inc., 101 Broad Avenue, Fairview, N J 07022). A Bird Film Applicator is used. A liquid puddle, approximately .75 in in diameter of both standard and the batch are poured on the upper area of the Morest Chart, side by side, with the standard on the right, then the Bird Film Applicator is pulled across the surface with a smooth continuous motion, to spread both liquids, at once into two 3-rail films, side by side. Similar colors or shades should have similar coverage, or hiding powers, or opacity. Instrumental color •natching utilizing colorimetry and spectrophotometry has not been widely used for nail enamels. Properly used, instrumental color matching may be of great value in the laboratory development of new color formulations and in production quality control. Many sophisticated tests and instruments may be used to measure properties such as hardness, adhesion, gloss, and internal stress, but experience has shown that a proper blend of objective and subjective evaluations are necessary in measuring the quality of nail enamel. For example, the wear resistance of a nail enamel is dependent upon so many factors that no laboratory test has yet been devised to demonstrate true wear resistance. Large differences in wear resistance may be determined by comparing a new nail lacquer to a standard applying to alternate fingernails of each hand and the standard to the other fingernails. Evaluations are made and recorded after four successive days of wear. When nail enamel meets all the test specifications, it is ready to be filled into bottles. The flashpoint of the usual grades of nail enamel is approximately 45øF. Since lacquers are highly inflammable (both the liquid and the dried lacquer film), filling, capping, and packaging must be carried out under fireproof and explosion-proof conditions. Proper precautions should be used as to no smoking, good ventilation, and proper electric wiring. CONCLUSIONS It has been shown that formulation of a nail enamel and particularly selection of modifiers depend upon performance requirements to be demanded of the finished

36 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS product. Compatibility of all components, both in solution and in film form places limitations on some formulations. In formulating a nail lacquer, therefore, one must accept some compromise between application properties and coating performance. Additives have pronounced effect on the physical properties of nail enamel films. The key to future developments in nail enamel technology is to find more effective modifiers for use with nitrocellulose. New modifying resins for enhancing gloss and wear properties are part of the continuing research and development effort in providing superior nail enamel formulations. Another approach is to provide a new product form exemplified by a recent patent granted to Greene et al. on aqueous emulsion nail coating formulations (6). REFERENCES (1) Linda Sojacy, Nail care takes two-prong approach, Advertising Age, p S28-29 (February 27, 1979). (2) J. Peirano, Other film formers for nail enamels, Amer. Perfum. Cosmet., 80, 35 (1969). (3) J. Peirano, Formulation and evaluation of nail laquers, Amer. Perfum. Cosmet., 80, 25 (1965). (4) A. A. Fisher, "Contact Dermatitis," 2nd ed., Lea & Febiger: Philadelphia, PA, 1973 p 232. (5) F. W. Busch, Jr., Gelled coating compositions, U.S. Patent No. 3 864, 294 (1975). (6) j. Greene, R. Nevin and M. Sharabash, Aqueous emulsion polymer nail coating formulations, U.S. Patent No. 4 158 053 (1979).