Reusing an Alum Mordant Bath

At great risk of becoming repetitious, I shall once again describe my current quandary. At this time of year, I mordant wool and silk in bulk, ready for the dye plant flowering season. Using 10% of the dry weight of the fibres in alum crystals, sometimes I hot mordant in a large pot of water by simmering for an hour, more often, I cold mordant by leaving fibres to soak in an unheated bath for 24 hours. Last week, I made a dye bath with dried Dyers Chamomile flowers and tried a direct comparison. The wool which had been mordanted hot took up more of the plant dye than wool which had been mordanted cold. I had to conclude that putting my new supplies through a hot mordant process would give me the best results.

Prior to that, when dyeing with birch leaves, I had discovered that increasing the percentage of alum premordant to 15 or even 20% made little difference. I understand that fibres will only pick up half the alum from any mordant bath, whatever the concentration, though I don't understand quite why that should be so. I like to use things up rather than throw them away and having read that alum mordant baths can be reused, I've got into a routine of dividing the things I want to mordant into seven equal portions. I weigh out and dissolve sufficient alum to mordant four portions and after I have finished either the hot or the cold process, I mordant the next two portions in the remaining alum, and finally, repeat the process with the seventh and last portion before chucking out the solution. 

Though I have been growing common dye plants and foraging for others for some years, I still get unexpected results when I am dyeing. This can be all very lovely and serendipitous or all very beige and disappointing, either way, I accept unpredictability, it adds to the thrill. This does not mean I am overjoyed to suppose that some of my duller and dimmer plant dye results may have been the entirely predictable consequence of substandard mordanting practice. I do prefer life's rich tapestry to be a rich tapestry.

This week's trial was a second comparison of hot versus cold alum mordanting plus a comparison of the outcomes of dyeing yarn mordanted in the second and third reuse of hot and cold alum baths. All skeins are DROPS wool, for both the hot and cold process, 50g yarn was mordanted in 5g alum, 25g was mordanted in the leftover mordant bath and then a 12.5g skein was mordanted after that. For the dye bath, I soaked and simmered 100g dried coreopsis tinctoria before adding 100g wool yarn. 

Here are the results. The two larger skeins at the top both had the first use of the alum, the topmost skein in a hot bath and the one below in a cold bath. As before, the hot mordanted skein is an appreciably deeper colour than the cold. The two skeins in the middle were mordanted in the second use of the hot and the cold alum baths and the the two at the bottom had the third use. The very last skein from the third use of the cold bath was left more than 24 hours, I forgot to take it out so it soaked for two days. That one is a slightly darker ginger. I have peered at the others and held them up together and I cannot really tell them apart without reading the labels. They are all much the same as the skein from the first use of the cold alum mordant bath. Which is good news. It suggests I can reuse my alum solutions without sacrificing even more quality of plant dye results and that quite possibly, leaving things to soak for more than 24 hours will improve the results from all my cold mordant baths.

My companion, Elinor Gotland, came upstairs to help me sort through my stash.
"It's high time you cracked on with mordanting all this stuff, Beaut. June is busting out all over the garden."
"At least I know what I am up to now. The expensive yarns can have first go in a hot alum mordant to ensure the best dye results. Then for the others, I'll reuse the remaining bath cold rather than heating it over and over again, because there doesn't seem to be much difference between results from hot or cold reused baths. All the wool and silk tops will have a cold mordant because it works well enough and won't risk felting them. When I reuse the alum cold, don't you think I'd be better off leaving things to soak for two days rather than one?" 
That last question was disingenuous. As I cold mordant things in the household bath, three uses of alum for 48 hours apiece would put the bathroom out of action for nearly a week, which might be pushing my luck. Happily for me, Elinor was too busy fossicking about with my stuff to put two and two and two together.

"What about this beautiful length of heavy tweed from Cambrian Wool?"
"That will have to be mordanted cold because I haven't got a big enough pot for the whole thing and I don't want to cut it til I've decided what it is going to be."
"Oh, I can already picture its perfect destiny, Beaut. These base colours are bound to suit me. I think you should overdye them with Goldenrod and make me a tailored jacket and matching bag."
"All that from half a meter?"
Elinor bridled.
"I have a very slender physique once my fleece is shorn. This summer, my stylist has suggested a dynamic short cropped back and sides with shag cut locks framing my face. A contemporary spin on the gamin style I used to favour in my catwalk days in Paris."
A diplomatic nod seemed safest. I'll just scour the tweed and see how much it shrinks. Elinor's modelling career ended some time ago and she may discover June has been busting out elsewhere.