I've been learning a lot about the chemistry of henna in the last few years. One of the most confusing and notable things about henna is the apparently contradictory information on pH. Henna powder needs a mildly acidic solution (pH of about 2-4) in order for the dye to be "released" from the plant material. What that means is that the dye molecule (lawsone) is attached to a sugar molecule in the leaf. A process called hydrolysis breaks the sugar and lawsone apart so that its free to do its job. The next thing that happens is that the lawsone attaches its self to cellulose (in the case of paper and cotton) or keratin (in the case of skin, hair, and silk.) This happens by a reaction called Michael Addition which prefers alkylin (above a pH of 7) environments. So, lawsone requires a low pH to be made available for use, but a higher pH in oder to be used! What can we do? Here's what I did:
I soaked one craft stick in ammonia (A) and the other was left alone as a control (C.) The pictures below show the result immediately after removing paste, several days later, and after exposure to heat several days after removing the paste.
We can see clearly that the ammonia soaked stick is darker, especially at first. We can also see that with the addition of heat and time, the stick that was not soaked in ammonia nearly "caught up" with the other. This brings me to the conclusion that the dye will attach to the wood even in a neutral envirnonment it just takes more time. You may also notice that the color is warmer in the stick that was not soaked. In the end, you may prefer not to use ammonia on wood if you like the warmer color. If your in a big hurry, on the other hand, you may want to give it a try!
15 comments:
i realise this is an old post but i was wondering - how long does the henna stain stay on the wood?
Forever!
As long as you leave the paste on several weeks two several months.
Don't use essential oils in the mix because they cause bleeding. Don't use sugar because that makes it too hard to get the paste off. If you have to chisel and scrub you buff the stain right out while getting the paste off!
Very cool. Can you recommend a finish for it?
I like acrylic lacquer because its easy to use and doesn't risk yellowing. polyurethane is a good choice too, but I suggest a water based polyurethane. Solvent based polyurethane undergoes a chemical reaction that may change the color of the stain in unpredictable ways.
You can also use a stain between the henna staining and finish if you like, just make sure to choose a very light color so you don't loose the contrast between your art and the wood.
Interesting! What ingredients did you use in your henna paste? Have you attempted to dye a larger surface area a solid color?
Ingredients for this paste is just henna powder and lemon juice. Very simple!
I have done large solid areas, but I have done large boxes in patterns.
I build furniture and am looking for an alternative to commercial stains. They are so toxic, and so is the clean up. I bought some henna hair dye and am going to try mixing that to stain the wood. If I immediately seal w/ polyurethane after scraping off the paste, do I still need to wait weeks or months before scraping off the paste? Thanks so much!
The color of the stain depends on how long you leave the paste on. If you don't leave it on long the stain will be orange. Leave it on some weeks for a light brown, and some months for dark brown.
Even after you remove the paste, the color will continue to deepen for some time, but when the paste isn't left on for a good month or two... or even three, will never get as dark as when the paste has been left on, no matter how long you wait.
You can seal as soon as you take off the paste, and the stain will continue to mature.
i want to decorate henna on paper and posterboard.. what do i seal it with henna design. will henna spread on the paper/ posterboard or do i apply something before then apply henna..
There's two different ways to do henna on paper. Either way you want to make a paste without essential oils or sugar and make the paste a little stiffer than usual. This keeps the henna from spreading and bleeding.
The first method involves leaving the paste on forever and sealing it in with a spray sealant or carefully painting over it with mod podge.
The other way is to leave the paste on for a few days, iron it with a dry setting on your iron, then gently remove the paste. This method doesn't require a seal.
Hi, I wandered on to your site looking to do the same as Nick - dying wood furniture. I was wondering if you knew if it would be ok to leave the henna'd wood unsealed? Would this react to air after a while / stain clothes etc? Thanks! Isabelle
You'll want to removed the paste (probably after several days) which will stain the wood permanently. After scraping away the paste, the color will be fairly pale and rusty. Over the course of weeks or even months it will deepen and darken. You may leave THAT unsealed with no worries that it will wear or rub off on clothing, etc.
If on the other hand you mean to leave the paste ON the wood, yes, you do need to seal it or it will begin to crumble and fall off over time.
Hope that helps!
Yes that is very helpful, thanks! Isabelle
Hi Jen,
Can I use it to make patters on cream coloured cotton curtains.
And should I use a fixative for future washing? I actually came here looking for wood dyeing, but you've already answered that and because I live in UK it rains all the time so I guess that's out! ��
Hi Lu, you could use this method on cotton curtains too! The trick is to leave the henna on the fabric for a month or more, then when you remove the paste, let them darken for several months before you you wash. When you do wash add something such as washing soda to raise the pH, and wash them HOT with as little agitation as possible. Keep in mind, only cotton for this method! Wool and silk will also take henna stain well but need to be treated more gently.
Please note, my blog has moved to hosting on my own web site. You can find the more modern version with more recent updates here: http://www.hennamuse.com/musings/
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