COLORING WITH SEMIPERMANENT DYES 383 hair involves the reducing of some of the disulfide linkages of cystine to sulfhydryl groups and bonding a water-soluble reactive dye to the sulfhy- dryl group. In one procedure (21), an aqueous solution at a pH of 9.0 containing 15% surface active material, 4.5% thioglycolic acid, 3.0% urea, 107o lithium bromide, and 10% Procion Black HGS is applied to hair for 10 min, followed by rinsing. Another procedure is described where permanent waving and dyeing can be com. bined in one operation. A method described in another British patent (22) includes a preliminary treatment with peroxymonosulfuric acid followed by application of an alkaline solution of the reactive dye. In a U.S. patent (23), fiber-active dyes containing the --SSOaH group are used following a reducing treat- ment. An additional treatment with a blocking agent is included, after dyeing, in order to block irreversibly any residual SH group. Aldehydes, quinones, and vinyl sulfones are included as some of the materials that are suitable blocking agents. The purpose is to prevent the redyeing of this hair and confine the subsequent coloring to that portion of the hair that has grown out since the previous dyeing. This process includes the following treatments all at room temperature: A 2% aqueous thio- glycolic acid solution is brushed on the hair and left for 15 min. Next, a 3% aqueous solution of the reactive dye at a pH of 9.0 is applied in the same way and left for 30 min. After rinsing, a 2% aqueous solution of formaldehyde is brushed on and left for 15 min. This is followed by rins- ing in warm water. Sulfur Dyes The use of sulfur colors for dyeing hair has been proposed in a British patent (24). The method, like that used for vat colors, involves conver- sion to the substantive leuco form, application to the hair, and slow dry- ing during which the color is developed by atmospheric oxidation. The aqueous dye solution contains 0.4% sodium hydrosulfite, 0.6% anhydrous sodium carbonate, and 0.5% Sulphosol dye.* After slow drying the hair is rinsed and dried. Certified Dyes The certified colors are those listed as suitable for foods, drugs, or cos- metics by the U.S. Food and Drug Administration and are manufactured under carefully controlled conditions. Although they have been used for hair tints for many years they have had no practical application for * Sulphosol dyes are solubilized sulfur colors, James Robinson & Co. Ltd., Hillhouse Lane, Huddersfield, England.

384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS semipermanent hair coloring. A method has been described in a U.S. patent (25) for the use of certified acid dyes in such a way that the color is claimed to be resistant to shampooing. In this method, use is made of an aqueous solution at a pH of 8.5 to 12.5 with a salt and carrier present. In one example, the aqueous dye solution contains 0.5% D & C Brown No. 1, 3.8% benzyl alcohol, 4.0% sodium sulfate, and 4.0% ammonium hydroxide. Preoxidized Pyridine Compounds A method of dyeing hair with preoxidized pyridine compounds is de- scribed in a recent Canadian patent (26). In one example, the aqueous dye solution contains 1.8% 2,5-diaminopyridine dihydrochloride, 0.8% (25%) ammonia solution, and 0.1% hydrogen peroxide (33%). The so- lution is allowed to react for 10 hours to form the pyridine dyestuff. Thereafter the solution may be filled into packages ready for use. In another example, the oxidized pyridine compound is filtered off, dried, and is then used as a semipermanent dye. Miscellaneous Components In addition to the dyes, the semipermanent coloring solutions contain surface active materials, solvents, thickeners, and often dye carriers or boosters. No attempt is made to list all of these materials but some of the important ones, with references, are listed in Tables I-IV. Table I Surface Active Materials Used in Semipermanent Hair Dyeing Name Type References Triton X-100 Nonionic 20 Tween 80 Nonionic 20 Igepal CO-730 Nonionic 20 Pluronic L-64 Nonionic 16 Sarcosyl L Anionic 16 Triton X-200 Anionic 21 Igepon T-55 Anionic 20 Sodium lauryl sulfate Anionic 20 Arquad 2HT Cationic 16 Cetyl pyridinium bromide Cationic 2 Aromox DMCD Cationic 16 Cetyl trimethylammonium bromide Cationic 13 Miranol SM Amphoteric 16 Deriphat 151 Amphoteric 27