I am a natural dyer but I also enjoy reading about and cooking food. I was recently perusing Michael Ruhlman’s book, Twenty: 20 Techniques, 100 Recipes. The first chapter is titled “THINK: Where Cooking Begins”. The author talks about the importance of thinking to the cook. I might say the same thing about the dye kitchen. Dyeing is not just about following a recipe, but thinking about and understanding the role of each of the ingredients.
Ruhlman recognizes that his list of techniques includes many that are also ingredients: salt, acid, sugar… One might say the same thing about our dye ingredients: mordant, acid, base, or dye plant… Awareness of what each ingredient contributes to the process is key to understanding how it fits into the larger picture of dyeing.
Let’s talk about mordants – alum specifically.
The alum we typically use in the dye studio is potassium aluminum sulfate [KAl(SO4)]. It is most likely made in a laboratory, is in powder or small crystal form, dissolves easily, and contains no contaminants such as iron.
Aluminum sulfate [Al2(SO4)3] is made by a different process and may be contaminated with small amounts or iron. The first dyeing I ever did utilized naturally occurring alum gathered from the ground surface – no telling how impure or contaminated it was.
We often shorten the name of our mordant to simply “alum” but there are many different types of alum and it may be best to use (and specify) potassium aluminum sulfate. I never purchase from a supplier who cannot provide material with that specific name.
Potassium aluminum sulfate bonds with the dyestuff and makes an insoluble lake INSIDE the fiber. Without this insoluble bond, the dye can wash out. This is why we don’t put dye, alum, and fiber in the same pot; inevitably some of the dye will bind with the alum in the bath OUTSIDE the fiber. That would be a waste of our dye and mordant.
The traditional approach to mordanting and dyeing is broken down into two steps. 1.) The alum is applied to the fiber. 2.) The fiber is dyed in a second bath, attaching the dye to the mordant and making the lake inside the fiber.
It’s important to get the mordant INSIDE the fiber. That is why we pre-wet and heat wool so that the scales will open up and the mordant goes inside. Otherwise we have ring dyeing, with the mordant and dye just sitting on the surface.
I have lately learned to dye silk using the Japanese approach of “middle mordanting” with Dr. Kazuki Yamazaki. The fiber is first dyed, then mordanted, and then re-immersed in the dye. This approach didn’t make a lot of sense to me until I experienced it and observed that it accomplished the same thing as pre-mordanting. The dye and mordant still go into the fiber and make the insoluble lake there. It’s a slower, quieter process which has the potential of building up layers of mordant and dye on the silk. This process is not suitable for wool.
Some things to THINK about:
- Alum is acidic – a useful thing to remember.
- Once a fiber is mordanted, it is always mordanted. The mordanted fiber can be dried and stored indefinitely.
- The more dye there is, the more mordant is needed.
- Alum can be removed with a stronger acid, such as citric acid.
- I typically use my alum at 15% of the fiber weight but I always test a new source of mordant in order to be sure that the strength is the same. Test by mordanting, dyeing, and observing.
- Potassium aluminum sulfate is an excellent mordant for protein fibers. I would take a different approach to mordanting cellulose.
- When a dye lake is made OUTSIDE the fiber it results in an insoluble pigment.
- When a dye lake is made INSIDE the fiber it results in an insoluble pigment.
- How the mordant and dye are applied to the fiber is very important.
Natural Dye: Experiments and Results 
When you dye first, then mordant…do you need to replenish the original dye bath before the final dip in dye?
No. But if you were to build up more successive layers of mordant and dye I would replenish.
I’m glad I ran across your article. Thanks so much for educating me about this technique. I will adapt these ideas and learn more about dying my reeds for basketry. I think now I understand why the colors fade in my reeds. I’ve been doing the entire process wrong. I plan to study this technique more thorough. Again, thanks for sharing!
I’m glad I ran across your article. Thanks so much for educating me about this technique. I will adapt these ideas and learn more about dying my reeds for basketry. I think now I understand why the colors fade in my reeds. I’ve been doing the entire process wrong. I plan to study this technique more thorough. Again, thanks for sharing!
There are many reasons why a dye might fade. Yes, the mordanting is an important part of it, but the choice of dye is also another factor.
Hard to believe the color shift!
That’s the difference between dye alone and the presence of mordant plus dye.
thank you!
Great post, thanks Catharine!
Is this the same method that is described In Natural Dyes sources, tradition, technology and science (Dominique Cardon) on pages 17, 18 and 19?
It is! Thanks for bringing that to my attention. I never connected with the process until I had a chance to do it.
Catharine
FanTASTIC! There’s so much misinformation, old wive’s tales and kitchen scrap nonsense around that it’s good to see the real science of it!
Hi, This is very useful information thanks. What will be your approach for mordanting cotton or linen?
Cellulose typically needs tannin combined with mordant for immersion dyeing. It is something I talk about in my book Woven Shibori. The new edition, focused on natural dye, will be re-released this coming summer. In the meantime, Maiwa is always a good source of dye/mordant instruction.
Thank you. This is the clearest explanation of the mordant process I’ve ever read.
Glad to hear it!
Catharine
Hi Catherine. Thank you for always sharing your valuable insights in natural dyeing. In your experience, would you prefer to use Potassium Aluminum Sulfate over Copper Sulfate as mordant for natural dyes?
In our Textile Institute in Manila, our engineers recommend Copper Sulfate. But I would like to know what works for you best and what could be certain issues in using Copper Sulfate. Thanks!
Copper sulfate has been used a lot in the past as a mordant. It tends to bring out the green colors in some dyes. BUT most of us have stopped using it as a primary mordant because of it’s toxicity and the environmental impact of its disposal.
Alum is much safer.
Catharine
Thanks again, Catharine! That is something that I will now keep in mind. 😀
i’ve observed this effect in ecoprinting…the technique i discovered years ago with eucalypts and which has since become wildly popular using whatever leaves are to hand. if the print isn’t brilliantly visible on the first reveal then, provided the bundle has been tied tightly enough so that there has been contact, then post dye dipping into a mordant of some kind will “develop” a hitherto “invisible” print. particularly amusing is a post printing dip into indigo, where the alkali of the vat can produce spectacular results, and a dip into iron (the metal, not the salt) = vinegar solution develops the cloth much like a black and white photo (but in this instance you need to rinse in fresh water when the desired depth of pattern has been reached, otherwise the whole thing just goes black).
:: india flint
Thanks India. These are good insights. I wonder what the chemistry is that causes the indigo to cause such results. This kind of dyeing is just full of discovery at every stage.
Catharine
Hi India, Yes, I experienced that all kinds of tannins will react to over-dyeing with indigo in a spectacular way. Recently I saw indigo with dye from fresh sumac leaves (on branch) resulted in almost Kelly green.
Hi Catharine, your thoughts on mordants are so deep and insightful. I love it. Friends in Oaxaca requested Michel to cover mordanting, co-mordanting, auxiliary treatment, or pre-treatment, especially on cotton. But the workshop at the 10iss is too short. Yoshiko
Hi! I’d love to know more about middle mordanting. In the experiments I’ve tried, soaking dyed things in a mordant bath had ended up with most of the dye leaching out into the mordant bath, and the wood ash lye seems even more prone to this than alum. How do you apply the middle mordant? Do you soak it, heat/cool it, paint it on…? (My soaks haven’t gone well and I’d love some pointers.)
The process is another whole lesson in dyeing but very briefly, the dyed goods go into a mordant bath (without rinsing) for a while and then back into the dye bath (after rinsing out excess mordant). You can keep building layers of dye and mordant by adding additional dye and mordant.
Thanks for this great analysis. Very helpful.
I’m so glad to hear that this is resonates!
HI, i m maruti from india . i had doing sappanwood dyeing . cellulose fibre do not penetrate the dye molecule . its absorbancy very low . as well as fastness properties also. washing fastness very poor.its getting 2-3 . & light fastness is 3-4 . how to maintain its fastness .without fadding .
pls share me .
I found this exceptionally useful! I love to know the whys behind the process so that I can adapt. Thanks for sharing your wisdom.
Understanding the “why” has always been important to me as well. My studio practice includes asking questions and trying to find answers.