Henna chemistry
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Posted by Catherine Cartwright Jones on September 07, 1999 at 02:08:29:
This is excerpted form "Formulation and Function of Cosmetics" translated from the German by G.L. Fenton, author Dr. J. Strphan Jellinek. Published by Wiley Interscience, 1970 "Henna is the most important ingredient of vegetable hair dyes. The word is arabic for the dried leaves and branches of the bush Lawsonia alba L. (also Lawsonia inermis L.) The substance responsible for the dying capacity of henna extradt was isolated by Timmasi (1916) and indentified as 2-hydroxy1,4-napthoquinone; the common name is Lawson. "Henna may be applied in various forms: in one it may be extracted with boiling water and pured several time over freshly washed hair. More permanent coloring is achieved by applying a paste made from henna powder and boiling water and leaving it on the hair until the desired shade is obtained. Finally, henna may also be mixed with shampoo, but it does not fully develop its effectiveness in this way since it works best in an acid environment. Henna extract is intensively red. The color left on the hair is orange red. However, this color appears only on white hair. Generally, a shade is obtained in which the natural color of the hair plays an important part. Combination of henna with other vegetable extracts or with metallic salt colors yields varying shades. Combining henna with a metallic salt improves its adhesion to the hair; the salts act as a precipitating agent and form stronger links with the hair keratin. "Even henna by itself henna has a strong affinity with hair keratin. ... Henna (which is often unpleasant in application) also adheres strongly to the nails; women in Middle East and India dye their palms and soles with it as well." In the following material the molecular map (I don't remember what those things are called....it's two hexagons with letters and 3 sticky-outy things with more letters) of the dye is included, I can email you the gif, just ask. His point in discussion of several potential keratin dyes is that though hair and skin SHOULD be responsive to the same dyes that wool is....you cannot boil the dye into hair or skin as you would boil dye into wool. "It is necessary therefore, to look for dyestuffs with smaller molecules and no "hooks": " The Lawsone molecule is very small, and is easily taken into keratin or collagen at body temperature (better if that temperature can be raised a bit). The one thing that goes in faster is the smaller molecule "PPD" That's why the PPD black stains so fast. Unfortunately, that little molecule slips WAY in and causes dermatitus and all sots of havoc! I can also copy out more of this and email it to you, it's more technical than I can easily make sense of......., and would be an awfully long post. If you want it, just ask. The structure of PPD is also covered in his material....and I can email that gif to you, too. It also explains why hennaeing over bleached hair makes it a vivid green.....it has to do with a blue dye part of the quinone that normally doesn't penetrate, but will dive right into very porous bleached hair and make it vivid green..
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