382 JOURNAL OF THE SOCIETY OF COSMETIC CItEMISTS Solvent-Soluble Dyes There are two types of colors that can be classed as solvent-soluble dyes. The first, which are the true solvent-soluble dyes, are insoluble in water and include compounds belonging to the azine, azo, anthraquinone, acid-base dye complexes, and azo-metal complexes, all of which are free of solubilizing groups (15). They are applied to hair as 0.5% aqueous dis- persions at an approximate pH of 7.0. The second type of solvent-soluble dye is the dispersed color which was originally developed for dyeing cellulose acetate and consists of mix- tures of solvent-soluble dyes and dispersing agents. They are applied to hair as 1 to 2% aqueous dispersions at a pH of 5.0 to 9.5. Their applica- tion is described in a British patent (15) and in a recent article by Sardo (16). Naphthoquinone Dyes According to a U.S. patent (17), 5,8-dihydroxy-l,4-naphthoquinone (naphthazarin) is applied to hair from a 0.25% aqueous dispersion con- taining ethanol, diethylenetriamine, a surface active material, and a thick- ening agent at a pH of 9.9 to give a strong purple color. In another U.S. patent (18), the application of 1,4- and 1,2-naphthoquinone from an aque- ous solution containing a surface active agent and a thickening agent at a pH range from 8.0 to 10.5 is described. The dyeing of hair with mono- amino 1,6- and 1,7-dihydroxynaphthalenes using a 1% aqueous solution at a pH of 8.0 is described in a British patent (19). In another British patent (20), naphthoquinone imine dyes such as basically substituted 5- amino-8-hydroxy-l,4-naphthoquinone-l-imine are covered. These are applied from a 0.25% aqueous solution containing a solvent, surface ac- tive material, and a thickener at a pH of either 9.9 or 3.5. Fiber-Reactive Dyes As the name implies, the fiber-reactive dyes are fixed on the hair due to the presence of reactive groups in the dye molecule. They are avail- able under the trade names Cibacrons©, * Procions©, * Reactones©, * Dri- marenes©,õ Remazols ©, and others. The application of reactive dyes to * Ciba Chemical 8c Dye Cmnpany, Fair Lawn, N.J. 07410. ? I.C.I. (Organics) Inc., Charlotte, N. C. 28211. • Geigy Dyestuffs, Ardsley, N.Y. 10502. õ Sandoz Inc., Hanover, N.J. 07936. I• American Hoechst Corp., Mountainside, N.J. 07091.

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.