So Ilana - my new online friend - suggested that maybe there is something that could be added to a dyebath to neutralize the tannins in things like pokeberries, where you don't want the brown color which comes from the tannins but the bright color that comes from the other chemicals in the dyebath to effect whatever it is you're dyeing.
I started by asking my mom, because she was trained as a chemist many, many years ago, if she knew anything about it, but she came up blank.
So I asked my friend Zinzi. Zinzi is a nurse with a 4-year BSN degree, but that's not the end of her career path, just a stepping stone. Nursing is her fall-back plan... She's fabulously ambitious and so smart it's scary. She's getting ready to go to grad school at UCLA or Johns Hopkins so that she can eventually do research into infectious disease or viruses... Her ultimate unlikely (and she knows it) dream is to discover the mythical panacea, the universal medicine, which will cure any ailment known and unknown to humankind. She knows a lot about chemistry...
She said that there *should* be some way to neutralize the tannins in dyebaths, since they are essentially types of acids (though apparently, not all tannins are tannic acid, that's just one type of acid in the family of tannins). Essentially, tannins bond to proteins with no intermediaries (don't need mordants) and this is why henna dyes skin, hair and nails so well (and wood and wool, if you're so inclined to try it). It's also why the bog mummies get so well preserved in swamp muck, which is full of tannins, and why a lot of dyes will eventually wash to a brown that doesn't wash out... The tannins permanently bond to natural fibers. She wasn't sure what would neutralize tannins, just that there should be *something* that will do it.
So I've done some research...
To quote (page 30): "Although the ability to precipitate protein is the defining characteristic of tannins, the detailed chemistry of the interaction is still only partly understood. It is now clear that both the type of interaction and the strength of interaction are dictated by both the chemistry of the tannin and the chemistry of the protein. In addition, the interaction is influenced by the reaction conditions including temperature, pH, solvent, composition, and tannin [to] protein ratio."
This would make sense to anyone who has ever used henna to dye skin. When dyeing skin with henna, it is generally recommended to use sugar, lemon juice and tea or coffee (both of which contain tannins) to produce a better henna paste. Lemon juice is used to make the pH more acidic. Sugar is used to make the henna stick to the skin better without crumbling. And it is generally recommended to wrap the henna pasted skin in cotton and cover with a sock (to raise the temperature) and let it remain over-night while you sleep. But still, the final result of how long and how dark the henna dyes the skin depends on how fresh the henna is and how it reacts to the individual's skin chemistry. This is also why henna paste used in theme parks and similar places does not usually stain skin well. They usually use water mixed with henna powder to make the paste, and it is usually very old and/or poor quality.
So I'm still not completely sure how to neutralize the tannins in a pokeberry dyebath. Zinzi suggests determining the pH of the tannins and neutralizing them with a base. But now that I think on it, perhaps this is where the suggestion that adding soda ash (sodium carbonate) to pokeberry dyebaths will help with the fastness of the dye comes from? Since soda ash is a base... How much soda ash, I don't know... but I've also heard that making a pokeberry dyebath completely neutral or alkaline will ruin its ability to dye... so there must be some acidity maintained. The pH of pure soda ash is 11.4 by itself. Assuming that the tannin in pokeberries is tannic acid, from what I understand, pure tannic acid has a pH of approximately 3.5. Considering that, and that we don't want to end up with a base solution, a weaker base than soda ash might be better for neutralizing the tannic acid.
Okay, I'm not a chemist... and I couldn't even do a titration properly in my high school chemistry class... But I would think that the first thing you'd need to do is neutralize the tannins in pokeberries if you don't want them turning anything brown. If I had some pokeberries to work with right now, this is exactly what I would try. I would use a weak base solution, such as water-diluted soda ash solution with maybe just a little vinegar added to be sure, and pour that over the pokeberries in a dyepot. Smash them. Then let that sit for a while at room temperature, so that the base might have time to neutralize the tannins, if it's able. Then I'd add the vinegar to help extract the dye and bring the pH back down to definitely acidic levels. (To be absolutely sure about all of this, I recommend getting one's hands on pH papers to test what the pH is doing at each stage of the process and record it for future reference.) The rest of the dye process, I would continue as normal. Fermenting a few days, straining the solution off, adding mordanted wool, simmering, cooling overnight, drying, rinsing... Not sure if the washfastness would be improved at all... I would guess that it would not, since most berry-derived dyes are not very washfast.