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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