COLORING WITH SEMIPERMANENT DYES 387 perature, a large percentage of dyes developed for the textile industry would fail to pass this test. Shelf Life The dye solution, ready for application to the hair, is aged in a sealed bottle for 1000 hours at 50øC. One manufacturer (20) has suggested that the samples should be aged for double this time, or 3 months at 50øC. A sample of natural white hair is dyed with the aged solution and the color compared with that obtained previously with the same solution be- fore ageing. Fastness to Removal on Shampooing Fastness to shampooing is determined by soaking the dry-dyed hair in a concentrated shampoo solution for 5 min at room temperature, and rinsing throughly with warm water. The amount of color lost is esti- mated visually by comparison with the untreated sample. Scalp Staining A stripe of dye solution is placed on the inside of the forearm and al- lowed to remain there for 30 min. The arm is rinsed thoroughly with running water and dried with a towel. The amount of staining is ob- served and recorded. Most acid and basic dyes stain the skin substan• tially. Behavior When Mixed with Other Dyes Acceptable shades of hair colors are formulated with mixtures of dyes and their behavior is tested on hair swatches and heads. Effect of Prior and After Treatments The effect of bleaching and permanent waving both before and after dye application is determined on swatches and heads. The effect of con- ditioners, cream rinses, and hair setting solutions applied after dyeing is also important. Evaluation of Colors on Models Using Half-head Tests By the use of half-head tests direct comparisons are made of the results obtained with any new formulation with that produced by a commercial product that has wide acceptance in the trade. These tests are used to determine uniformity of color from tip to root section of the hair, sham- poo fastness, color build-up, and scalp staining.

388 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Determination of Toxic Properties of New Formulations For the smaller companies, this is generally done by well-established testing laboratories both on animals and human subjects. The larger companies maintain their own special laboratories for this purpose. As was pointed out by Wilmsmann (32), in dyeing growing hair diffu- sion of the color into the fiber is hindered by the low temperature of dye- ing, the high viscosity of the dye solution, and the restriction of move- ment of the dye in solution caused by the fact that it is applied by brush- ing rather than by immersion. Penetration of the dye into the hair fiber can be increased by swelling the fiber, the use of carriers, the adaption of the electrical potential of the fiber to the state of the electrical charge of the dye ions, and by decreasing the size of the dye molecule. INDOPHENOL AND INDAMINE DYES The plan of the research reported in this paper was to prepare dyes having as small a molecular size as possible and test them for application as semipermanent hair colors. The indophenols and indamines (some- times called indoanilines), which are basically two substituted benzene rings connected by a nitrogen atom, are among the smallest dye mole- cules known. Because of their poor stability they have little value in the textile field except as intermediate products in the manufacturing of sul- fur colors (33). Most of the recent attention to the indophenols and indamines has been directed towards their use in color photography (34). While the simple indophenols and indamines are generally of insufficient stability to be practical for use as dyes, it has been shown (35) that the introduction of halogen or alkyl groups yields dyes of enhanced stability. In our research, many substituted indophenols and indamines were prepared and screened for their substantivity for hair, light fastness, and shelf life. Substantial retention of color by the hair, a fastness to light of 10 hours, and stability of the dye solution for 1000 hours at 50øC in a sealed bottle were selected as minimum standards. Since it is likely that most of these prepared indophenols and indamines would fail to pass one or all three of these tests, it was decided to use only these tests in our evaluation and designate those dyes that pass for further consideration. Since all of the indophenols and indamines that were prepared belong to the class known as solvent-soluble dyes, it was decided to apply these three tests to a substantial number of the solvent-soluble dyes listed in the Color Index (33), in order to determine the type of result that could be expected. This was done using 93 regular solvent-soluble colors. Of