HAIR COLORING MODERN FORMULATION CONSIDERATIONS 303 formulated so as to be completely removable with just one application of shampoo since they are surface phenomena and are very often completely indifferent to the condition of the hair whether it is normal, freshly bleached or just permanent waved. These advantages are of immense interest to the hair chemist. Because it is almost impossible to discuss this subject without using pro- prietary names or revealing company secrets, I shall stretch a point some- what and use rhodamine stearate as a specific example even though it is not too typical of the general class. The complexes of acid dyes wash off the hair much more readily than those of basic dyes such as rhodamine. Also, producing the very finely dispersed complex in situ as is generally done in actual practice, results in better effects than are obtainable by simply melting a pure complex such as D.C. Red 37 and trying to incorporate it into a product. -(C•Hs)2N f/•/O•l•--N" (C.2H5)2 C1 •/J•(••/) -[- CHa(CH,)ioC0--• ,•COOH Cationic D & C Red 19 -1- Anionic Soap --• (C•U•).,N-- /O,N•N - (C•H•)• L O D & C Red 37 Figure 2.•--Rhodamine Stearate viewed as an anion-cation complex of D & C Red 19. - (00CC•7H:•.O Rhodamine itself (Fig. 2) is seen to be a cationic quaternary ammonium compound. It is normally made by the reaction of the free base with hy- drochloric acid. If that same base is reacted instead with stearic acid, the result is known as rhodamine stearate, D.C. Red 37. These are the normal methods of manufacture of these two certified colors. However, it is ob- vious that a precipitate of D.C. Red 37 will also result if solutions of the cationic D.C. Red 19 and the anionic sodium stearate are mixed together. Finally, it is evident that the ionic charges shown on the classic structure of D.C. Red 37 in Fig. 2 cannot exist, because the material, being insoluble,

304 JOURNAI. OF THE SOCIETY OF COSMETIC CHEMISTS does not ionize. It is a color complex with some properties strikingly different from. the soluble parent color. These differences lessen as the complex is solubilized and the parent color can ionize once again. Rhodamine itself is exceptionally substantive to keratin, giving strong dyeings which are very difficult to remove, as one unhappy manufacturer of pink cold wave lotions discovered a few years ago! It will also stain the skin quite deeply, thus being of interest in some types of lipsticks, but un- fortunately it will stain the scalp just as nicely and so does not excite the hair colorist at all. In contrast, rhodamine stearate (when properly dispersed) is also quite substantive to keratin, but tends to give water insoluble transparent surface coatings which can be removed much more easily, depending on the pH from which they were applied. Confining the dye to the surface also means that ]ess will be needed for any given apparent depth of shade on the skin or hair. These facts may give pause to the lipstick formulatots who use D.C. Red 19 as a stain and then add a little soap to their paste to stiffen it up. On the other hand, it may be useful to know that many waler soluble certified dyes are usable in lipsticks if they are first complexed in such a manner. What we find to be true of the anion-cation complex of rhodamine can be generalized to all such color complexes. In effect, we are producing in situ modifications of the dyes to suit our purposes. Among the cationic agents used to precipitate the certified and other acid dyes in today's color creme rinse formulations are the following: 1. Surfactanls with a qualernized nitrogen, such as the quaternary am- monium, pyridinium or quinolinium compounds. More rarely, Julfonium and phosphonium compounds have been explored for the same purpose. This general group is often used i,n the alkaline pH range to reduce irritation and to give better color yields. 2. Tertiary amines, especially the fatty amines, can be used. They usually give most satisfactory results in media which are slightly acid to neutral. 3. atlkylolamides, not normally considered cationic, will give desirable complexes in very acid (usually below pH 4) media. The Kritchevsky con- densates seem to work better for this use. In general, when working with these complexes, it must always be re- membered that the state of the dispersion is all-important. A perfectly useful combination will suddenly lose much or all of its color yield value if too well solubilized with nonionics. Yet if you do not solubilize it some- what, an awful precipitate may form, leaving ugly blotches of color on the hair which will rub off all over the place. A perfectly innocent nonionic gum may be added to the formulation to help suspend the dispersion, but unless it is added at the right time in the manufacturing process to keep the particle size of the complex at a particular point, it too may reduce the