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

EVALUATION AND TESTING OF NAIL LACQUERS 333 the problem of ease of application is the rate of drying of the lacquer. If it dries too rapidly, even appli- cation is difficult. If the film dries too slowly it may be necessary to wait too long before applying the second coat and it may be too long before the hands may be used after applying the lacquer. The rate of drying of a new lacquer may be compared with that of a standard lacquer by making simultaneous pours on glass and observing the time required for each to become dry to the touch. In order to make a truly valid comparison the viscos- ity and the total solids of the lac- quers should be the same in order that films of equal thickness may be formed. For absolute comparison this test should be carried out under conditions of constant tem- perature and constant humidity. Constant temperature and humidity rooms are not usually found in cosmetic laboratories. However, relative drying rates may be ob- served in the ordinary laboratory by making simultaneous pours. The drying time observed on the glass plate pours will be very different from that actually found when the lacquer is applied to the nails. The glass plate drying time will be six to eight times as long as the time required for the same polish to dry on the nails. The more rapid rate of drying on the nails is due to effect of the body heat. The nails are of course at body temperature at all times. For this reason a check of the drying time of the new lacquer compared with the standard lac- quer when applied to the nails should also be made. The gloss of a polish is another factor which the customer takes into consideration when com- paring two nail polishes. In the laboratory the pours which have been made on glass plates for the purpose of comparing drying times may also be used to determine the relative gloss of two nail lacquers. The Hunter gloss inspection lamp can be used to give usef•ul com- parative values for the gloss. The most important charac- teristic of a nail polish as far as the customer is concerned is its wear resistance. Unfortunately wear re- sistance is not a function of any one nail polish characteristic. Several factors are involved in the general attribute called wear resistance. In use the polish must withstand excur- sions into the depth of my lady's hand bag, trips into the office fines, and general contact with objects in the environment. There is no question but that the hardness of the film is a factor in the wear resistance. However, it does not follow that a harder film will give better wear for the film must also have the proper flexibility. Harder films are usu- ally less flexible and may there- fore give poorer wear. A Sward Rocker may be used to test the rela- tive hardness using the same films which were used for observing drying time and gloss. Not too long ago a survey was published showing the relative value