Last month we had some serious storms. On a blowy Sunday, himself and I took the dog out and found a fallen silver birch tree. I was well pleased, took my penknife out and started peeling a branch, himself soon got bored and walked on with the dog.
I went back next day to strip another branch and ended up with a whole kilogram of fresh bark which I shared out between three pots and left to soak for a week. Bark dyes are sensitive to changes in pH and shifting the dye bath pH to alkali is recommended to improve the colour. Unfortunately, alkali does not improve wool fibres, it weakens them and makes them feel rougher.
This seemed a good opportunity to test out how much or how little alkali would get the best results from silver birch bark dye. I dissolved a heaped teaspoonful of soda ash in hot water and added it to one of the three pots of soaking bark peelings, before leaving them all to ferment. The following day, the fluid in the alkaline pot was already much darker.
I added enough soda ash to bring one of the acidic pots up to neutral pH 7 and simmered them all for an hour before taking out samples to look at the dye bath colours and to double check that the pH had remained the same. The photo shows samples of baths at pH 5, 7 and 9. The deep colour in the alkaline jar looked by far the most promising.
In the meantime, I had been shopping on eBay, looking for some durable chunky wool yarn at a decent price. I was well pleased with my five 100g skeins of British wool from woolbothy. As advertised, they were not smoochy soft, being worsted spun they were sleek and a little stiff, handling more like cotton, but well structured and neither rough nor hairy.
I divided them into ten 50g skeins, gave them a hot soak with detergent to lift off the dressing, then a couple of plain water rinses. No mordant is needed for bark dyes. Three skeins went into each pot for an hour of simmering, then I took one skein out of each pot and boiled the rest, to see whether keeping bark dyes simmering below the boil really mattered.
Here are the results, rinsed in plain water after drying out for a couple of days. In the front row, the skeins that had about an hour simmering, in the back row, the skeins that had a further boil and stayed overnight in the dye pot. On the left, the acidic pH 5 skeins, in the middle, the neutral pH 7 skeins and on the right, the alkaline pH 9 skeins. This is a good strong wool yarn, acid had made the beige skeins smoother while the deep brown yarn from the alkali bath felt slightly roughened, a little squeaky, but still nice enough to handle. All the wool was puffier and softer after washing, dyeing and rinsing than it had been when I first bought it. My conclusions - it is definitely worth testing pH and getting an acidic, fermented bark bath up to neutral before dyeing, but going for a strong alkali is counterproductive, unless you like brown or you are dyeing plant rather than animal fibres. The colours are deeper after boiling and longer steeping, I'd say keeping below the boil isn't critical, though I like the pink from the pH neutral simmer best and I would hesitate to boil a wool that was prone to felting, such as merino.
Having two of each of the deeper dyed skeins, I decided to modify them with copper as I like that better on silver birch than modifying with iron. The final three skeins were heated in a new pot of water with a slug of homemade copper acetate solution - just offcuts of copper piping left in a mixture of water and vinegar. This one has been quietly dissolving all winter and currently has a strong blue.
The copper modified skeins from each pH dye bath are shown in the back row of this picture. Six small skeins of silk were dyed together with the wool and they are shown on top of the front six skeins of wool.
One last and rather important test before embarking on a multicoloured project. I knitted a swatch with three rows of each colour and put it through a 30 degree wool wash cycle in the washing machine using a handwash liquid detergent that is pH neutral. Happily, thorough washing had no ill effects, the colours that had been dyed at different pH stayed just as they were.
Outdoor photography gives a truer impression of the pinkness of birch bark dye. Plus it was fun to tit about with wool in the woods now the days aren't quite so cold.