MORDANT MONDAY: Exhausted Mordant Baths + Sumac Tannin

We get mordant questions all the time at Botanical Colors so why not create Mordant Monday??? Got mordanting questions? Email [email protected]

YOU ASKED: After watching your video about aluminum triformate I decided to order it and started using it. I work with large quantities and large pieces, so I prepared a bucket with 50 liters of water and 500 grams of aluminum triformate. I used it to mordant approximately 5 kg of yarn/pieces. The water was white at the beginning, I suppose because I just mixed the powder, but after the first load, it was just like regular water. I used it again with 2 kg of yarn, and after that it looks a little murkier but no sediment at all. I think I might need to add more AT. What am I supposed to look for in the water to know that it is time to add more? Is there some kind of testing/checking maybe with PH strips, to see if there is still AT in it? My regular water has a PH of 7 and this one is 4. One last question, you recommend to wear gloves, does that mean that the AT can affect your skin or is it just out of habit?

KATHY ANSWERED: Our experiments showed that with 20gp/l aluminum triformate in a 10 liter bucket, we were able to reuse the bath 10 times before recharging with 10 gp/l additional mordant. In your case, you are using the mordant at 10 gp/l, and you are using much more material than we did in our experiment so you may be close to needing a recharge. We recharged at 50% of our original amount and topped off the container and the color yield was good.

If you are doing production dyeing and need to repeat the results, you can also calculate the amount of mordant from your wof and measure that amount out, allow the goods to soak overnight cold, then remove, rinse and dye. The mordant bath could be saved and reused for non-production purposes. Repeat the calculation with a fresh bath for your next production mordanting. We have tried 5-10% aluminum triformate on wof and it has worked very well.

The mordant bath is somewhat acidic and drying to skin. We use gloves to protect our skin.

YOU ASKED: I see on instagram someone bundling what I think are sumac leaves I assume to be then steamed to release tannin. I thought the highest level of tannin was in the red “buds” and that they must be gathered before there are rains to apparently dilute the tannin. What do you know about tannins in sumac?

KATHY ANSWERED: Sumac has been used historically to tan leather and all parts of the tree are used, so leaves, bark and fruit will all have quantities of tannin. The berries can be used for dyeing and are also used as a spice (za’atar) and to make “lemonade”. I don’t know what part of the tree contains the most tannin but the commercial sumac powders we use seem to be mostly from leaves, bark and wood. Apparently poison sumac looks a lot like sumac so be aware of what you are harvesting!

YOU ASKED: Is there a way you can you tell if a mordant bath is actually “exhausted”, or is the 50% recharge just a general rule of thumb? I’m looking at mordanting items for production, and was just curious if there was a limit to the amount of times you should be reusing and recharging the mordant bath? Currently using baths of both homemade aluminum acetate + chalk and also tannin + homemade aluminum acetate

KATHY ANSWERED: First, I’ll talk about exhaustion. My experience is that if I’m reusing the mordant bath without recharging, there is a point where the color yield from my dye bath turns out lighter, even with the same amount of dye, fiber and dye process. To me, this means my mordant bath has weakened and should be recharged or a fresh bath made. Of course, if you are a production dyer, this type of experiment is a little frustrating because you haven’t hit the color that you wanted and now need to do some type of rework or color correction.

So in order to provide guidance on avoiding the above problem, we talk about recharging the mordant bath to save water and mordant. The recharge rate is going to differ somewhat but the 50% recharge amount is really a general recommendation. If you find you get equal results with a 25% or 30% recharge, then make note of that and use it in your own practice.

The mordant bath isn’t exhausted after one use and some information I’ve seen says that there’s still at least 50-70% of the mordant remaining in solution, so there’s plenty in there. Sometimes I will use a mordant bath twice with no recharge and am not able to discern a difference. We have customers in water conscious locations that regularly reuse their mordant baths 5-7 times. It’s really when the mordant liquid becomes incredibly cloudy and “thick” that it should probably be disposed of and a fresh bath made. You may be able to keep your mordant bath going longer with your homemade aluminum acetate, so do some experiments and keep good notes and you’ll find what works best for your production needs.