Natural Dyeing Take One: Alum Mordanting with Heuchera Plants

I read in the Ravelry forums that the root of the Heuchera plant was rich in alum and could be used as an alum mordant. Since my mum had quite a few heucheras in her garden that she was going to relocate, I cunningly convinced her to part with a few of the roots. Well, actually it wasn’t all that hard since heucheras are quite willing to grow and spread and you don’t need much of the root for the plant to happily be relocated. They’re usually multiplied by cutting up the roots.

So my mum and I went down to her heucheras for a bit of a cull. She’s not exactly sure of the variety but it is the most common one in France apparently. She also has a few more of fancy varieties, but wasn’t quite so willing to uproot those quite yet…

Heuchera plants (specific variety unknown) before we uprooted them

So I took some of the roots, washed peeled and got a whopping 230g of prepped roots:

Heuchera roots at different stages of stripping

The Ravelry discussion was quoting Nature’s Colors – Dye from Plants by Ida Grae which suggested that ‘two finger-lengths of alum root will mordant about one-half pound of yarn’ (Grae 1979: 53). I measured two finger-lengths and took it to weigh about 15g. What I didn’t realise at the time (and which only occurred to me quite a while after I’d done the whole process of mordanting a couple of mini skeins) was that I’d taken two finger-widths rather than two finger-lengths… mmm… yes, I can be that dumb quite easily… I then recalculated that two finger-lengths should represent about 60g of roots. Of course since no two roots are the same and different people have fingers of varying lengths, this is all an approximation and this is where the experiment begins. I’m taking my stupid error as another point of comparison with only 1/4 of the recommended amount for alum root mordanting. My second batch of heuchera mordanted yarn rectified this mistake. If 60g was enough for half a pound, then 200g of roots could mordant 750g of fibre.

I chopped my roots up and decided to freeze 30g to experiment with later, since the maths would be simpler with exactly 200g of roots left to boil. I wasn’t entirely sure what Ida Grae meant by ‘pre-cook alum root’ so here is what I did: I simmered my prepped roots in a litre of water for about an hour (no, it wasn’t that I didn’t quite realise how long it had been…), then let it soak overnight. Since it had boiled down quite a bit I added another litre of water, and simmered it again the next day for another hour. The liquid was clear to start with, translucent red after the first round of cooking and quite a muddy pink on the second round.

Cooking the roots, before, after first round, after second round and strained

The liquid had reduced quite a bit and once the roots had been strained out, weighed 300g. These 300g contained the alum of 200g of roots, so enough to mordant 750g of fibres. We therefore calculated that 4g of the concentrate would be necessary to mordant 10g of fibre.  To make calculations easier and to be on the safe side we decided on 5g per 10g of fibre. Halving the amount of weight of dry fibres we wanted to mordant was therefore giving us the amount of Heuchera concentrate we needed to use.

France 2011

Unmordanted vs. heuchera mordanted yarn, copyright Eddieduckling

We then proceeded to dilute in cold water enough of our concentrate to mordant our sample skeins. We soaked our sample skeins in water first to get them thoroughly wet, then squeezing excess water out we put them in the pot with the mordant, and set it to simmer for an hour. We then let the wool cool down in the mordant and rinsed it once cool. There was a clear difference in colour between the wool which had not been mordanted and the one which was heuchera mordanted, even with the lot which was only 1/4 of the recommended amount. The heuchera mordant certainly added a dusty pink hue to the fibre.

We still have to test our skeins for ligtht and wash fastness obviously, but the heuchera mordanting definitely reacted differently with the colours from the alum mordanting, as you’ll see in the coming posts.

Photos of our dyeing experiments are being collected in a Flickr group come and take a peek.


Grae, Ida (1979) Nature’s Colors – Dye from Plants. MacMillan Publishers.


2 responses to “Natural Dyeing Take One: Alum Mordanting with Heuchera Plants

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