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

STABILITY TESTS ON MAKE-UP ITEMS 307 is likely to do that, laboratory tests are in order to avoid rejects. OILY MAKE-UP This type of make-up has become fairly common in recent years. It is a make-up which is quite hard to direct pressure but readily liquefi- able on rubbing. Such a product must be checked for its tendency to crack and for objectionable sweat- ing. In order to test for cracks, the make-up is subjected to a rapid chilling either on ice or by pouring ice water over the cake. The ex- tent of sweating is tested by sub- jecting the make-up to the influence of extreme changes in temperature between 10-110øF. Under these conditions there should not be enough beading to run off the sur- face when the make-up is standing on edge. It is also a good test to place the make-up in a deepfreeze, allow the shrinkage to occur and then try to knock out the product. If that can be done, it usually means that during the winter months com- plaints will be received that the compacts have come loose from the base. COSMETIC SUSPENSION In this group we have some liquid make-up, leg make-up, and nail lacquer. Sedimentation and change in viscosity are properties to be watched especially in this group. Sedimentation volume is determined by centrifuging or by measuring the height of sediment over a period of three months. Change of viscos- ity is readily determined by Ford or dupont cups, on old and new samples. Naturally the tests which have been described here have been modified by chemists in the cos- metic industry in different ways. Constant alertness on the part of the laboratory will hold trouble and complaints at a minimum. It is poor policy to shrug off complaints, because a few complaints in the introductory period may mean hundreds of them when the product has been on the shelf for varying lengths of time and has reached many consumers with different ways of using the cosmetic. Members who have not received Volume II, No. 3, please advise the Editor at once. The issue was printed in England and mailed from there.