152 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS closure to form a red azine dye (eurhoidine) as in the following reaction: NHs NHs NHs NHs NHs NH % % % + Nits CHa CHa p-Phenylene m-Toluylene Blue Diamine Diamine Indamine NH• xT NH• CHa Red Azine (Toluylene Red) This may explain another problem that has long plagued manufacturers of oxidation dyes. This is the tendency of drab shades based on p-phenylene diamine such as black, ash brown and ash blonde, to develop an objection- able reddish cast on the hair. Para phenylene diamine may contain very small amounts of meta diamine and the small amount of blue dye resulting during oxidation actually contributes to the desired drab tone. However, this blue dye in the hair can slowly undergo further oxidation and end up as a red azine dye. Although the stability of the blue and purple in- damine dyes can be improved by the careful use of polyhydroxy phenols, there is considerable room for improvement. It is a popular belief that one of the great advantages of oxidation dyes is that they produce fast shades on hair. This is not quite true. As we pointed out, shades which make use of the meta diamine coupling reac- tion tends to fade or turn red on the hair. Drab shades tend to lose their drabness and some of the red shades fade out. A careful study of the prob- lem results in the conclusion that good color stability is achieved when all of the dyes formed in a hair shade are of the azine, oxazine or phenazine type. Here we have complete oxidation and ring closure. Poor color stability is found when the hair shade includes indamine or indophenol dyes which can undergo further oxidation. It must be remembered that it is possible to produce a specific hair shade with more than one combination of intermediates and certain combinations result in more stable shades. This is by no means a hit or miss project. A thorough understanding of the ac- tion of intermediates individually and in combination with other inter- mediates is necessary to successfully formulate hair dyes. One of the problems in the laboratory dyeing of hair is that the dyed hair swatches are not always stable over a long period of time. One cannot

COLOR REACTIONS OF OXIDATION DYE INTERMEDIATES 153 use as a permanent reference sa•nple a dyeing on hair of a dye intermediate or mixture under the specific conditions being evaluated. How can we know if a dyeing we make today is the same as one we made six months ago using the same dye composition ? We have tried color photography of dyed hair swatches but without great success. The spectrophotometer shows considerable promise especially since the development of newer in- struments and techniques. We have found that skeins of spun silk can easily be dyed with metallized and milling silk dyes to match very closely hair dyed with oxidation dyes. Even very delicate variations in shade and intensity can be matched. These dyeings on silk are extremely fast so that they can be kept as a permanent record. We will admit, that matching oxidation colors on silk in this manner requires considerable skill. THE EFFECT OF MOLECULAR SIZE To color hair, oxidation of the dye intermediates must take place on the hair. If oxidation and dye formation is completed before application to the hair, color absorption will not take place. It is generally believed that the absorption or diffusion of dye into human hair is controlled by several chemical and physical factors including the molecular size of the inter- mediate. Small molecules can penetrate the intermicellular spaces of hair--large molecules cannot. An excellent discussion of this by Wilms- mann (4) was recently published. During the hair dyeing process, dye intermediates of relatively small molecular size penetrate the intermicellular spaces of hair and are oxidized to insoluble dyes within the hair shaft thereby locking the dye within the hair. It is quite possible that the molecular size of components of the dye base or vehicle plays an important role. The composition of the dye base has a pronounced effect on the depth of color of the dyed hair, as well as on the actual shade and highlights. For example, if a dye composition were prepared in an aqueous-alcoholic solution, a liquid soap base, and a super farted cream base, all at the same pH and dyeings made on hair for the same length of time and under identical conditions, the color intensity would vary greatly. The water-alcoholic solution would probably give the most intense dyeing and the superfarted cream color the weakest dyeing. As the swelling of the hair increases, it becomes more receptive to the dye and the degree of swelling is certainly a contributing factor. The viscosity of the product may also affect color diffusion. Another possibility is that some of the intermicellular spaces are blocked by large fatty molecules in the dye base thereby reducing penetration of the smaller dye intermediate molecules. This can be demonstrated by using alpha naphtol with p-phen- ylene diamine or with p-amino phenol. In a series of dyeings from a soap base and a superfarted base, both at the same pH, the soap base resulted in dyeing of higher intensity.