Dyeing with Black Beans (& Mordanting with Alum)

I promised some black bean dyeing quite a while ago, and do not think I have forgotten! But before you do any dyeing, you have to mordant – and the mordant used for black beans is common enough that it really merits a post of its own (unlike vinegar mordanting, which to my knowledge is pretty much useful only when dyeing with berries). But the black bean dyeing is down there, so keep scrolling if that’s why you’re here. So without further ado, I give you:

Step 1: Mordanting with Aluminum Sulfate!!! (with sidekick Cream of Tartar)

You will need: Aluminum Sulfate, Cream of Tartar, a large pot that you will NOT use again for cooking, rubber gloves, water, your stove, your wool.

Mordant is important to the natural dyer. The natural dyer is stealing colors from nature – colors made from naturally found chemicals that, for the most part, serve other purposes in their natural state than changing the hue of fabric or fiber. The purpose of mordant is to make those natural chemicals bind permanently to their new homes, generally by changing the PH.

Several chemicals can do this, but the most popular are Aluminum Sulfate, Copper, Tin, and Chrome. Since they each do different things to PH, using them results in getting different colors from your natural dyes. Also, some are more appropriate to some dyes than others. However, they are all fairly serious chemicals. I like Aluminum Sulfate (commonly referred to as alum by dyers and the like) because it is the least harsh as a chemical and it is reasonably priced in bulk.

Tip: You can get alum from dye suppliers, but the cheapest way to get it is from your local nursery, if they have it. (Gardiners use it to change the PH of soil to make some flowers bluer.) The 4 lb. bag above I got from Grandfather’s Garden Center in Columbia, MD cost me 9 bucks and has mordanted 16 lbs of wool. (That’s a lot.)

The first thing to do is to weigh your wool, then measure out the appropriate amount of alum.

The magic amount of alum to use is 1/4 weight of fiber. That means 1 oz. of alum for 4 oz. fiber, 4 oz. alum for 1 lb. fiber, etc. Sources vary on the amount of Cream of Tartar to use, but I generally go with about 1 Tbsp per 4 oz. fiber.

(This stuff is not record-setting dangerous, but it is smart to use rubber or latex gloves. Also, when you pour it out it can create a big chemical cloud that makes me nervous, so do it outside, with a mask, or at least at a distance.)

Once the chemical is measured out, the next thing to do is dissolve it. Add a decent amount of very hot water and stir until it’s dissolved, then add cold or lukewarm water to fill the pot to the point that will probably cover your yarn or fiber.

Then just add wool (or yarn or alpaca or whatever) and heat! Your goal is for the solution to simmer for about 1 hour. Exercise caution: I will say it again – these are real grown-up chemicals. COVER this while it’s simmering, and when open it to check on it, do not stick your face in the fumes. This is not wassail, people. After an hour, turn off the heat and let it cool overnight.

The mordanted fiber can be used right away the next day, or you can squeeze it out and lay it flat to dry. (Use gloves while it’s wet – see above bit about chemicals.) Once it’s completely dry you can put it away until you’re ready to do some dyeing.

Step 2: Prep the Beans

You will need: Dry black beans (4x weight of fiber to be dyed), cold water, lots of bowls, long wooden or plastic spoon.

If you have ever used dried black beans, you know you have to soak them overnight – and you may have been surprised or horrified to find their soaking liquid black and disgusting the next day, and your bowl turned blue. Guess what: that liquid is a dye! Black beans are delicious, and they are delightfully cheap. And one of the semi-convenient things about this dyeing method is that it partially prepares an enormous batch of chili.

Tip: If you happen to live near one of those cool organic grocers where you can get dry goods in bulk, organic black beans actually work even better for this. Not like it should be surprising – fewer chemicals on the surface of those dye-yielding black skins.

The key is to use a LOT of water. You want to be able to completely fill your dyepot later with just the water you’ve soaked from your beans. This means a lot of bowls. They will turn a little blue and yucky inside from this process, but it’s nothing a few runs through the dishwasher won’t fix. And it’s just beans and water at this point, so you can use containers you still want to use for food later (unlike your dyepot, which handles mordants).

When you first put the beans in to soak, they will look unassuming, as in the picture above. But after a few hours, give them a stir with a long wooden spoon.

Weird like Aunt Irma’s beard! But that’s your dye. And stirring is your friend: stir often. Stir right before you go to bed. Stir right after you get up. Stir when you walk past the bowls. BUT: DO NOT STIR for a couple of hours before you are ready to dye. Color is not the only thing stirring into that water; you’re also getting some bean particles that you really want to settle to the bottom of the bowls.  Those beany bits have proteins that will turn your beautiful blue into a much less interesting gray.

Step 3: Dyeing the Fiber

You will need: Prepped bowls of beans & water, dyepot, mordanted fiber, latex gloves

Tip: I usually prep the beans this while my mordant pots are boiling – then I let the mordant pot cool overnight while the beans soak and am ready to dye in the morning.

When the beans have soaked sufficiently (less than 24 hours if you want to use the beans for anything else), skim all the fluid out of the bowls into the dyepot. Try to do this without disturbing the beans at the bottom too much; you don’t want those proteins getting into the water you’re skimming off.

Tip: since no chemicals have yet touched these beans, you can still use them for cooking! Cook them up now and can or freeze them, or just freeze them as-is. I put them in gallon ziploc bags with enough water to cover them and lay them flat to freeze into massive bean-blocks.

For this example, I am using some beautiful grey wool from Breezy Willow. If you use white, of course you will get a truer blue hue than I did in this case, but the resulting color is always on the grey side, in my opinion. In other words, there’s no way to get deep or royal blue with this stuff.

Add the mordanted wool to the dyepot (using gloves if it’s still wet with mordant water) and… leave it to sit. I suppose you could boil it, but everyone I got info from just let it sit on the porch or under a sunny window for a few days. I would do it outside, but we got a couple of frosts last week, and I’d really rather not deal with frozen wool.

Leave it for at least a few days. I’ve left it for as long as a week (though in that case, cover it – critters. I won’t say more.)

Rinse thoroughly, lay flat to dry out of direct sunlight, and glory in the beautiful grey-blue you’ve just created.

If you are dyeing unprocessed wool, you will get some natural variation. For some reason, this dye takes more to the greasier tips of fleece locks than the cleaner bases. Carded up, it all blends into a slight heather. When dyeing yarn, I like to only put half the hank in the dyepot and leave the other half out to drip into a bowl. The liquid will soak up through the yarn not in the pot (I think that’s called capillary action – any middle-school science teachers out there?) and give an elegant gradient.

Not happy with gentle grey-blue? Want a darker color than you’re getting? There are a few things you can do:

(1) Use the smallest container you can for the fiber, and only soak the beans in enough liquid that you’ll be able to cover the fiber. This will give you the highest possible dye-to-water ratio.

(2) Use more beans.

(3) Use superwash wool – it supposedly takes all dyes better, but I’ve only noticed a striking difference with this particular dye.

14 thoughts on “Dyeing with Black Beans (& Mordanting with Alum)

  1. That’s all very interesting…..esp. since I already did it! I can say I did the mordanting just right, and I almost did the black bean dyeing just right. The only thing I did not know was about not using the dye closest to the beans. But it makes sense…..the darkest dye came when I boiled 3 lbs of beans for an hour, then used a ladle to scoop off the top juice to dye my wool. The 2nd time I dyed with black beans, I only used 1 lb of beans and poured the juice through a sieve before using it as a dye….and it came out lighter.


  2. An adult student of mine did get a uniform, very dark navy blue with a high concentration of dye to fiber, all cold processed. She left it in the light for a few days and the color did not fade at all. A fifth grade student of mine got a fabulously streaky effect that appear to be the broken out components of the purple: it streaked into carmine reds, sky blues and navy blues into blue violet. The overall effect is that of a blue violet. I used heat and got a brown like a cooked bean, tasty, not useless, but not my intent.


  3. Can one use your typical grocery store alum for your mordant instead? I’m a little hesitant to use harsher chemicals. If so, how much would one use and would one add Cream of Tartar also? What about dying cotton fabric? Do you think it would take? Am attempting to make a series of dye samples on a pile of used white cotton dish cloths I found in a box and haven’t had much luck so far with red, green and black. The brown and yellow turned out great using coffee and turmeric. I wonder if there was some pre-existing finish on the fabric that is making it resist the dye. Will attempt green using red onion skins and blue using your black beans if the same magic happens on cotton as with wool.


  4. Hi Cecelia; I haven’t dyed cotton but I know you can. I have a vague idea of it taking due a bit darker than wool, but I don’t know where in my brain that is coming from. As for grocery store alum, no idea! As long as it is aluminum sulfate. I imagine the proportions would be the same. No matter what, be careful with those chemicals! Enjoy your experiments and let me know how they go!


  5. Grocery store alum IS aluminum sulfate. I get chemical safety and teaching the importance of following careful procedures, I really really do, but putting the fear of God into your readers over alum is unnecessary. It’s used in pickling! It’s used in vaccines! Obviously you want to avoid mega doses of the stuff but it’s safe to ingest and they sell it in the spice aisle of mousy grocery stores.

    To answer your other reader’s question, the usual amount I’ve seen recommended for use as a mordant, alongside cream of tartar, is 8% and 7%. In other words, for every 100 grams of wool use 8g of alum and 7g of cream of tartar. But the amounts don’t have to be exact. I’m curious to see what will happen if I go as high as 25% as you’ve suggested here.

    You can get intense blue from superwash wools, but that’s because part of their treatment to reduce felting includes an acid bath, to strip them of the microscopic scales on each stand of fiber that interlock and cause felting and shrinking. I’m curious to see what a full strength vinegar soak would do for the dye, either prior to or as part of the mordant process. I’ve also dyed roving that was a wool/silk blend and gotten different colors from the silk than from the wool, which was fun.

    For the reader looking for good greens and reds: bean dye is pH sensitive, so you can add a bit of vinegar to the dye itself and get a pretty red dye and a bit of ammonia or baking soda to get green. I know for certain that the green works as a dye, because I’ve seen the photos, but I’m not sure if the red does. My last batch of wool came out sort of a sage color, so I laid it while wet onto a paper towel that had been soaked with a little vinegar, and turned it a purple blue instead.

    Another way to get darker blues is to up the concentration of the dye. I’m sticking with two parts water to one part dry beans. I’m about to try a large batch with five pounds beans (about 15 cups) and two gallons water (a gallon is 16 cups so it’s close enough).

    Hope this information helps!


    1. Thank you for this detailed information! Yes, there is a LOT you can do by changing the PH, I just never got to the point of doing it on purpose. It’s great to hear someone else’s techniques. I’m glad alum is nothing to be skeevy about.


  6. I did a little more reading and it turns out there are several compounds called “alum”. The alum you get in the garden store, if it has any brown flecks in it at all, those are iron or iron oxide (rust) and they will have an effect on your color. Iron “saddens” dye by making the colors less bright, more somber and dull.

    Just got a copy of Wild Color by Jenny Dean that goes into detail on this.


  7. Does anyone know how to make the finished product color fast? I’ve read that exposure to sun and washing takes the color out.


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