PRESSED POWDER TECHNOLOGY 613 mixer to drive off the excess water before completing batches, so that the drying procedure is eliminated. In the dry process, the powder is subjected to compression without being wetted to any appreciable extent. Little or no liquid binder is required. Processing of pressed powders has varied considerably with the advent of pearlescent products. A considerable amount of experi- mental work is necessary to determine the proper mixer, mixing time, and milling or pulverizing techniques to be utilized in pressed powder technology. Color and pearlescent development is related to the amount and type of mixing employed. Pearlescent materials break down easily with overmixing and the change of appearance in the final pressed prod- uct is quite noticeable. Twin-shell blenders and the Littleford* mixer have been used successfully in place of ribbon-type mixers in producing powders. Hammer, pebble mills, and air mills have also found a place in pressed powder technology. After manufacture, the prepared batch should be pressed immedi- ately. If this is not feasible, bulk powders should be stored in double polyethylene bags inside airtight containers. Compression into pans is done automatically or semiautomatically with an air, hydraulic, or cam- operated type press, such as a Kemwall.? Pans are composed of steel, tin, or aluminum, depending upon product specifications. It is neces- sary to carry out trials to obtain the optimum pressure needed for each product. The pressure exerted by the press varies with the type of press used, and the amount and type of binder used, formulation type, and the shape of the pan. If the pressure is too high, the result is a tablet which is too hard, has poor payoff, and has a tendency to glaze. A very low pressure produces a soft cake, prone to breakage, which rubs off easily. Pressures usually vary from 300 to 2000 psi. Pearlescent products gener- ally are more difficult to press and require a higher pressure. Often pressures are varied to accommodate the type of applicator to be utilized with the product. It is necessary that the powder be uniform before pressing so that no air pockets are formed during compression. This causes the cake to break more easily. A ribbon of silk is usually inserted between the press- ing die and powder before each compressing action, to keep the surface matte and prevent shine. Generally, cake eyebrow, liner, and rouge are usually pressed hardest, eyeshadows intermediately hard, and face pow- der and blushers softest. Each type of product should have its control * Littleford Bros. Inc., Cincinnatti, Ohio 45226. 'I' Kemwall iDstributors, Ltd., Brooklyn, N.Y. 11223.

614 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS as to optimum hardness. Tablet hardness may be measured by using a penetrometer or some other tactile sensitive instrument. Tablet break- age may be empirically measured by drop tests from heights of at least 18 inches and shipping tests. Finished cakes may be also checked for shade control by application on skin, white paper, on a powder puff, or varia- tions and combinations of each aforementioned method. Attention shrould be given to the even filling of the pans in all cases where the pressure of the press is not self-adjusting, such as with a cam-operated press pressure trial adjustments are necessary to determine exact consis- tency and cake payoff. SUMMARY Retrospectively, it should be evident that manufacture of a successful pressed powder requires much experimentation, together with keen mechanical ability. The specialized machinery and technology required to manufacture these products successfully, the competition in pricing, the labor of manufacture, and the need for a wide range of shades and product prototypes are some of the reasons why very few cosmetic firms manufacture their own pressed powder products. (Received January 21, 1971) REFERENCES (1) Macias Sarria J., Processes of manufacturi•g crude make-up, Amer. Perfurn, 59, 11-2 (1944). (2) Janowitz, H., Compact make-up, Soap, Perrum. Cosmet., 28, 649-50 (1955). (3) Winter, F., Handbuch der gesarnten Parrum. Kosrnet., 2nd Ed., 1932, pp. 615-20. (4) Factor, F., U. $. Patent 2,034,697 (March 24, 1936). (5) Factor, F., U. $. Patent 2,101,843 (December 14, 1937). (6) Factor, F., British Patent 501,732 (1939).