[mehndi]

I hope someone can give me some help understanding how a lawsone molecule attaches to keratin when used as hair/skin dye, as well as the subsequent darkening over the following 48 hours.

A paste is made form the ground leaves of a henna plant (which contains about 1% of the dye lawsone) and lemon juice or water. The paste is left to stand in a warm environment for 4-12 hours. This paste is applied to the skin or hair and left on for several hours. During this time the dye absorbs into the hair/skin. When the paste is first removed the hair/skin is bright orange. Over several days this slowly changes to a deep red/brown. Over the course of about 2 weeks this color is slowly exfoliated from skin, but remains permanent in hair.

I have some questions about this process.

1.   Paste made from henna leaves and water will turn brown immediately and be ready to use within a few hours Paste mixed with lemon juice will remain green and takes as much as two days to be ready to use. I think that the color difference is caused by the ascorbic acid in the lemon juice reducing the lawsone (HQN) to THN. Does that make sense? Would this have an effect on the dyeing properties of the paste? Would lemon juice have an effect on the speed at which the glycosides in the plant matter break down in order to release the HNQ? In my experience pastes made with lemon juice make a dye that lasts longer, but it is much debated among henna artists.

2.   I have read that HNQ binds to keratin via  Michael Addition. Can you tell me where on a keratin strand this can happen? Can you show me a diagram? Would using water or lemon juice to mix the paste have an effect on this?

3.   What is happening when the stain on hair/skin darkens over time? Is it caused by oxidation? Does it have anything to do with the difference between THN and HNQ? Can you show me a diagram of this part of the process?

4.   Many people add essential oils to there paste. The ones that are high in monoterpene alcohols make the dye process much faster and achieve much darker color. What are possible causes for this?

I heartily thank you for reading this far! If anyone can offer any insight at all I'd be eternally grateful. I've spent quite a bit of time trying to figure this out with my peers, but... well, we're a bunch of artists. How far do you suppose we got? LOL

Jen Schafer
www.hennamuse.com

[Borek]

As for 1 - I would rather start with checking if it is not low pH that changes paste behavior. I can be completely off but that's first thing that comes to mind. To quote wikipedia:

100 milliliters of lemon juice contains approximately 50 milligrams of Vitamin C (55% of the recommended daily value) and 5 grams of citric acid.

[ARGOS++]

Dear Mehndi,

Lawsone (2-hydroxy-1,4-naphthoquinone = HNQ) is of the same Pigment-family as all the Anthraquinone and follows therefore the identical dying process.
Yes, Pigment and not Dyestuff, because Pigments are water insoluble and very stable dyes!

Their Dying-Process passes the so called “Leucoform”, where they get more or less soluble for the application. The following Oxidation (usually the Oxygen of the air is sufficient) the final Pigment is formed again/back.
In the Henna leaves the “Leucoform” is stabilised/blocked by Glycon, that’s why this “form” is nearly colourless.
When you prepare the past a process called “Fermentation” starts, what releases the “Leucoform” (you may call it THN), which immediately starts the very slow Oxidation to the final Pigment.

I have troubles to believe, that it will bound to Keratin inside a biological environmental, because as soon as the Pigment is formed, it will not be accessible for normal reactions, because it is not soluble anymore (without going back to the colourless “Leucoform”!).

Now I think we are able to answer your questions:
1.)   You see you are right. The lemon juice will influence the “Fermentation” in a few different ways and not only by chancing the pH. As longer it takes for realising as longer the past you can use, but you will never get the some high concentration of the “Leucoform” to migrate into the skin.
2.)   I think we have already answered it. Also lemon juice will not make it better.
3.)   Also this, - your answer is correct. You have to keep in mind, that the Oxidation by “Air” is very slow. You can speed it up, but your skin may be in danger therefore.
4.)   The final influence may be not absolutely clear for that. But for a darker/deeper colour effect it is required to get/use even higher concentration of the “Leucoform” and maybe a better transfer process into the skin, too.

Finally you may have realised, that you can go, at least partially, an alternative way, to get the most dark/deep dying of your skin, but it needs some chemical knowledge to not damage your skin!
It starts not with the Henna leave, but with the final pure Pigment instead.
 
I hope it may be of help to you!

Good Luck!
                    ARGOS⁺⁺

[mehndi]

Borek, I thought that too, but I did not get good results from a solution of plain citric acid, although the color of the paste was the same as with lemon juice. This is why I assumed that it was the ascorbic acid that was improving the color of dyed skin, but I suppose it could be any of the other things in lemon juice too. I do think the low pH is the cause of the green paste though.


Argos, Fermentation? Maybe I'm misunderstanding something. Fermentation is the break down of a sugar into energy correct? Lawsone is released when it is divided from a sugar molecule. Wouldn't that be hydrolysis and isn't that just a precursor of fermentation? If there is fermentation happening here it is of no interest to me because I'm not concerned with what happens to the sugar after its severed from the lawsone molecule.

Lawsone does in fact bind to keratin. I have a stack of papers here telling me just that.

lemon juice has made darker color in my tests. I was hoping you could explain why.

Is it possible that lawsone is soluble in the monoterpene alcohols in the essential oils?

I am a certified professional. I am certainly aware of safety issues.

Henna has been used for a skin and hair dye for 5000 years by using the leaves. I'm not looking to modernize the methods. I just want to understand them.

[ARGOS++]

Dear Mehndi,

“Fermentation” is not only if Bacteria eat “Sugar” and produce CO2 or/and Alcohol or an Acid.
Bacteria and Enzymes can do more, but for all of that you will have to ask a Biologist, and I’m not a real representative of them. For the formulas involved in this process you may visit the German version:

Hennastrauch (Wiki)

You will see there, that the “Leucoform” is bond over an Oxiygen-brige, like an Ether, to the “Glycon”. As an Ether is a quite stable Compound, I can easy imagine, that the “Sugar” needs first to be eaten up to break this particular bond. Otherwise a very special Bacteria or Enzyme would be required to do it.

If I remember correct, I never told that somebody cannot do a “Michael Addition” with Henna and maybe to a Keratin, if he/she is using the adequate condition. But I still believe, that in a biological environmental AND under living conditions, it must be nearly impossible, but especially not if one Reactant is a “solid body”.
 
Lemon juice can have a lot of different effects during “Fermentation”; if it will also influence the transportation process into the skin, and how, I don’t know.

But if we adopt, that only Henna will make the colour, then we have to accept, that only the concentration is left, to make the different “Shades”.
As “every” Brown starts its Concentration-Live (at the lower end) as a Yellow and changes by increasing Concentration to orange, then to orange-red, then to red-brown/yellow-brown, then to a real brown then to a dark brown, then to a dark gray-brown, and finally to black (if the required Concentration can be met), a Lot of the different “Shadings” can easily be understood.  How fine disperse the skin may present the Pigment, may have an additional small influence too.

Yes, the monoterpene alcohols may have an influence as better solvent then water and maybe influences also the Transportation process. Additionally their solubility of Oxygen maybe also lower, what keeps the “Leucoform”  longer stabile at a higher Concentration.

To give you an even more profound answer I have first to do some own additional investigations.
But at the moment, I can not spend time to do so.


So I hope to have been anyway of help to you!

Good Luck!
                    ARGOS⁺⁺

[Nigel]

I have just bought some pure lawsone. I Dissolved a small amount in methylated spirits (95% alcohol, 5% methanol), and dabbed it on my skin.

I expected it to go dark quite quickly, but nothing happened other than a slight yellowing, which washed off when I removed the solution. I tried ading lemon juice, but there was no improvement.

Can anyone explain to me what I should do with pure lawsone to get it absorbed by the skin?

Thanks

Nigel