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Alum is my Friend

If you haven’t done a lot of dyeing, this post won’t make much sense, but read along if you like.

When we last saw the black bean dyeing process it looked like this

After 2 days, the light purple colour had barely made an impact on the wool.

Last time, it took a night to become a lovely shade of blue–that wool was superwash though, and sock weight.  I had also dyed some thick 100% non-superwash wool, which became grey/blue over night.  This wool has 20% nylon in it, but that shouldn’t make it undyeable.

I rethought my process.  The first time, I had soaked the yarn in an alum solution for 30 minutes before I dyed it.  This time I skipped that step.  How important can a little bit of white powder be?

Very important it turns out!  I sprinkled some alum into the dyepot, stirred it around, then had a nap.

Amazing!  When I woke up, the colour of the dyepot had changed, and so had the colour of the yarn.

How does it work?

Alum is a mordant, it serves to fix colours in dyeing.  Mordant comes from the Latin word mordere (to bite).  It chemically binds the pigment to the cells that are being dyed.  Some substances require no mordant at all, and will dye fibers bright and vibrant colours through immersion, or boiling.  It turns out that black beans are NOT some of these substances (for the record, onion and turmeric can be used without a mordant).

I bought my alum at the pharmacy, it is ammonium alum.  You can also buy alum at the grocery store.  I don’t know if it is the same chemical though, or even if the results would be the same.

Wikipedia says: Alum (pronounced /ˈæləm/) is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrate potassium aluminium sulfate with the formula KAl(SO4)2.12H2O. The wider class of compounds known as alums have the related stoichiometry, AB(SO4)2.12H2O.

So…alum is a sulfate of some variety (not necessarily containing aluminum).  Alum has been used in water treatment, and in dyeing, and in pickling and as an aftershave, and on and on and on….

I now know that it is a really important ingredient when using black beans as a dye!

Lesson learned:  Alum is my friend!

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This entry was posted on Saturday, May 8th, 2010 at 3:41 pm and is filed under knitting. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.