EVALUATION AND TESTING OF NAIL LACQUERS 33I tribution to the human skin test is as conclusive as the actual use method. Finally, it must be re- of a material by large numbers of membered that no testing method people. EVALUATION AND TESTING OF NAIL LACQUERS* HENP, Y J. WING, PH.D. Northam l/Farren Corp., Stamford, Conn. As You ALL know, nail pol- ishes are nitrocellulose lacquers. The testing of nail polishes may be covered quite simply by stating that these lacquers should be sub- jected to the same tests as those applied to any lacquer of this type. However, this leaves the newcomer in this field quite at loss for the usual tests for lacquer are probably unknown. Before proper testing can be done on any product it is necessary to first determine the characteristics of a material which gives customer satisfaction. In a nail polish, color is probably one of the most im- portant properties. We also find that ease of application, rate of drying, wear resistance are all part of the customer reaction to any polish. Fortunately the chemist does not choose the color which is to be sold. This selection. is usually made by the-promotion department. The formulator simply makes up colors which he hopes will meet the re- quirements of those who make the * Presented at the May 18, 1951, Meeting, New York City. final selection. However, once this selection is made it is then the job of the production and control de- partments to see that every batch of this shade matches the standard selected. This standard needs to be estab- lished first. It is often done by using pour cards made by pouring a coating of the colored lacquer on white Bristol board followed, after drying, by another coat which leaves some of the first coat un- covered. This standard is pre- pared from a laboratory sample of the polish which has been approved for color. Experience has shown that the dry pour cards kept away from the light when not in use undergo practically no color change. However a liquid sample of the same polish will change color quite rapidly and will lose its value as a standard. Having established the standard it is necessary to compare the batch with this. Another pour card on similar stock is prepared using liquid from the batch. After drying this is compared with the original standard pour card and of

332 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS course should match. Color differ- ences can be detected by instru- ments. However, careful evalua- tion has shown that the trained color marcher can detect differ- ences which are not recorded by any instruments. A recording spectrophotometer will give a fine record if two colors are exactly alike. However if there are small differences the record will not be conclusive. In addition this in- strument will not tell the operator the type and amount of additional color required to produce a good color match. The shortcomings of instrumental color comparators are inherent in the machines. These instruments are able to observe only a very small area of the sample and under only one condition of lighting. The human color marcher observes comparatively large areas and is able to move the samples so that the incident light falls on them over the whole range of angles. This ability to judge very small color differences and to interpret these differences in terms of the adjust- ments required to produce a color match explains why the color marcher still holds an important place in the production of colored lacquers. The lacquer used for nail polish must not only be of the correct color, it must also apply properly. One characteristic which determines its ease of application is the vis- cosity of the lacquer. The viscos- ity of a lacquer may be determined in a number of ways and in various units. A viscosimeter of the Mac- Michae'l type may be used in which case the viscosity values may be determined in c.g.s. units. A more simple efflux type of viscosimeter will serve the purpose just as well. Instruments of this type such as the A.S.T.M. or du Pont cup are filled to the top and the time required for 50 mi. to flow out of the orifice is determined. Relative viscosities in terms of time in seconds are observed. Experience has shown that lacquers having a viscosity of 270-310 centistokes or 55 to 65 secends using the No. 10 du Pont cup have satisfactory application properties as nail polishes. It is necessary for the buyer of bulk nail lacquer to make certain that the viscosity is within the limits shown to have good acceptance by his nail polish customers. Many factors enter into the problem of producing a nail polish which applies easily. These are separate but closely interconnected problems. The vicsosity of the lacquer, which has just been dis- cussed, plays an important part. If the lacquer is too viscous it is difficult to apply a uniform coating, while if too fluid, it will flow too easily on the nail and run under the cuticle at the edge or pile up there in a thick layer. The shade of polish also plays a part. A very light shade which carries only a small amount of pigment is diffi- cult to apply so that it appears even, because any variations in film thickness appear as variations in depth of color. Another factor which enters into