STABILITY TESTS ON MAKE-UP ITEMS 305 velop an oder on aging. However, a good grade of zinc stearate should allow the rubbing into slightly per- spiring skin without developing a rancid or off-odor. Certainly, just smelling the dry zinc stearate will not give an indication of its keeping qualities. COMPACTED MAKE-UP ITEMS In recent years a number of cos- metics have been merchandized in cake or stick form. Of course, dry rouge has been with us for many years, but cake make-up and cron- pact powders are of more recent ori- gin. In these products breakage is probably the most important factor for rejection. To test the strength of compact powder, we use penetrometer and drop tests. The penetrometer needle drops from a height of 1 cm. onto the cake and its penetration is a measure of hard- ness. A cake of compressed powder has to withstand more than 10 drops from a height of 1 foot on a thin metal plate cushioned by a few sheets of paper. Some compacted powders have excellent cosmetic properties but are very fragile. Here we have developed a package tumbler which allows us to test the best way of packaging a more fragile product. The latter test is complemented by actual test shipment across the con- tinent and back. Face powders, either loose or compressed, are used with puffs many of the puffs are glued with latex, containing paper as a cush- ion, and for this reason the influence of ammonia and sulfur dioxide has to be considered. LIPSTICK The most important of all make- up items is probably lipstick. There are quite a few things and conditions which can make a lipstick unsalable. To name a few:breakage under use, excessive sweating, rancidity, loss of perfume, uneven shading, no staining, loss of stain, melting in the show case, attack of the case, or discoloration of the case on the lipstick. Every time a new reason or new conditions are found which are objectionable to the ulti- mate consumer, a test is set up to anticipate the encountered condi- tions and catch it before it leaves the factory. With this in mind, we have tests for melting points because we know that if the melt- ing point of a lipstick drops below 60øC., we will certainly have a number of complaints of melted and deformed lipsticks. Anybody who has given any thought to es- tablishing a melting point procedure for lipsticks has developed an in- feriority complex because, frankly, a lipstick mass does not have a melting point, for in the final analy- sis, all lipstick melting points are viscosity or plasticity measurements. Plastic flow is a question of tem- perature and pressure. When this is realized then the strictest ad- herence to prescribed testing con- ditions becomes most important. Usually each laboratory has its own "melting point" procedure and results are not interchangeable.

306 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Experience has shown that an oven test made on a lipstick stand- ing upright in the oven is not con- clusive. A better test is to oven test the swiveled-out lipstick lying on its side. Under this set-up the least weakness will cause a droop of the lipstick. A good lipstick should withstand this test in an oven of 45 to 50øC. Every so often there are com- plaints that lipsticks break while the woman is applying the lipstick to her lips. This breakage is only to a minor degree a function of the composition, but is primarily a function of the case, the diameter, and shape of the lipstick. For this reason, we use a test to determine breakage strength of a lipstick by clamping the lipstick swiveled out to its full length in its holder and then apply- ing, by means of a leather leash, weights until the lipstick breaks. The cutting test by means of a weighted thin wire gives some in- dication as to the application prop- erties of the lipstick. No com- pletely satisfactory test has been developed. One important test which indi- cates the stability of the lipstick is a rancidity test on the wax-oil base and on the completed lipstick. This test is conveniently done by the absorbed oxygen method. Four samples of lipstick are placed on a water bath and heated for predeter- mined intervals. A sample is taken from the water bath dissolved and ti- trated with sodium thiosulfate to determine the amount of absorbed oxygen. This gives us an indication of the probable shelf life of the lip- stick. This is an adaptation of the method developed for determining shelf life and rancidity of fats and oils. In addition to the common tests which check on the stability, it is sometimes necessary to look into the maintenance of properties such as application and stain. We have found that once in a while a lip- stick will stain considerably less than at other times. In order to catch these discrepancies, we have developed a stain test. For this test we use the gelatin film on an unexposed but developed photo- graphic plate. We employ such a test plate because gelatin is akin to the general class of proteins found in the skin of the lips. The gelatin on photographic plates is a care- fully controlled and uniform prod- uct. The test plate is soaked in water for exactly five minutes and then a glob of lipstick is pressed onto the plate and allowed to remain in contact with the gelatin for five minutes. In addition to tests on the cos- metic product as such, the inter- action between lipstick mass and lipstick case has to be considered. Some of these reactions are rather slow and become only evident after several months. Even acceleration in an oven does not seem to bring out the discoloration which is no- ticed only after months of shelf life. From time to time, the salability of a lipstick is reduced by excessive sweating, bronzing, fading of color, and blooming. These are not regu- lar occurrences but, ifa composition