Silver Birch Bark Can Dye an Equal Weight of Wool and Cotton

Last July, I made a dye bath by fermenting and simmering a couple of hundred grams of silver birch bark and it dyed all of this.

First into the dye bath was a 25g skein of wool yarn, which came out orange brown, so I added a teaspoon of soda ash to make the bath alkaline and a glug of home made copper acetate solution to bring up better pink tones. A second 25g skein of wool came out a deep red/brown and two small skeins of silk were dyed a paler shade. After that, I used the dye bath as a vehicle for simmering a rolled and tied silk scarf contact print and the exposed silk at the borders went a rather gorgeous version of the same colour. Over the following week, I used the afterbath to provide background colours for plant contact prints on a linen shirt and two cotton frocks, getting successively paler pinks. The wool yarn had had no mordant, but the silk scarf had been mordanted with alum and the cotton and linen had all been mordanted with aluminium acetate in order to take up colours from fresh dye plant leaves and flowers. I can't recall the total weight of materials dyed in that one bath, nor indeed how much bark went in it in the first place, but I was sufficiently impressed to take this picture.

Lately, I used a whole kilogramme of silver birch bark divided into three dye baths to study the effect of making the naturally acidic pH of a fermenting bark bath more alkaline. By the end of the process, the three baths had dyed a total of 480g unmordanted wool and silk yarn.

Afterwards, the pots sat out on the patio with the bark still lurking at the bottom. A week or so later, I poured all the contents through a colander into a bucket, dumped the bark on the border as a mulch and carried the bucket back to the house.
"You're not hanging on to that mouldy old dyebath, are you, Beaut? It's gone all slimy, you can't put any more wool in there." My companion followed me back to the kitchen and peered into the bucket. "Is that a drowned mouse?"
It was just a floating leaf, though I'll admit, the bark afterbath had become more viscous. It also looked a much deeper red than when it was first made.
"I bet this bucket is still full of dye, Elinor. I bet it will dye loads more stuff."
"I bet it's full of tannin from all that boiling and far too alkaline from all the soda ash you poured in."

Testing with an indicator strip showed the bucket of afterbath, two parts of which had been alkalinised for the first dye session, had become acid again. I added enough soda ash to bring it back to neutral pH 7, which made the colour deeper still, then called Elinor over.
"See, the bark must have gone on fermenting in the pots, the pH had fallen right back down. What a good job I didn't listen to you, you old doom merchant." 

My cup of triumph overflowed when another 100g skein of wool yarn had been simmered for an hour and came out pretty much the same pink as the original test skein which was simmered at neutral pH. 
"Now watch me dye loads of fabric, I don't even need to mordant anything." Elinor was busy chatting on the phone and just waved me away with a distracted hoof. After a good rummage in the cupboard, I came back downstairs with some offcuts - half a metre of cotton/linen blend curtain fabric in a natural beige and half a metre of white cotton curtain lining. They seemed pretty soggy after half an hour in the sink and appeared to go deep pink as soon as they had submerged in the dye bath. I lit the gas under the dye pot and shot back upstairs to cut half a metre off a heavy canvas curtain I'd been saving.
My companion saw me pass.

"Steady on, Beaut, at least give it a wash. Ych a fi, I can't believe that curtain was put away so grubby. Are you sure it's cotton canvas? Feels a bit stretchy to me." I just carried on cutting off the curtain rings, though I did put the whole thing through a hot wash before putting my cut half metre into the dye bath along with a glug of copper acetate solution. Once all the fabric was hanging up on the airer, I felt entitled to a very smug smile.
"Just think of the lovely pink project bags I can make with that."
"They'll be hand sewn, will they, Beaut? Seeing as how you're too scared to try using the lovely sewing machine your mother left you."
Rather ostentatiously, I put another 100g skein of wool into the dye bath.
"I'll get to it, Elinor, that machine is just more complicated than my old one. This fabric will inspire me."

Only this fabric looked rather odd once I got it down a few days later. The dye was wildly uneven on the cotton and had sat on the humps and disappeared from the creases in the heavy canvas. Worse was to come. When I put it in the sink, the dye flooded back off of it. Usually, if things are left to cure for a few days, relatively little colour is lost on rinsing.

"That rinse water's going to take a while to run clear, Beaut." Elinor sipped her tea. "Doesn't look like the fabric was properly soaked before dyeing."
This was not a great day in the life of Rushworth. Watching another load of dye disappear down the plughole, cutting my losses, I put all the material in the washing machine, then the tumble dryer. That last skein of wool had come out of the bath a very pale version of the first, but in between dyeing the two, much of the colour from the dye bath seemed to have sat on the fabric, rather than fixing to it.

I liked the pink anyway.
"If I add up all the weight of this wool and fabric together with the 480g of yarn I dyed before, that kilogramme of silver birch bark has dyed 1.26 kg of fibres."
Elinor looked at me under her specs.
"Really? You call this last skein of wool 'dyed'?"
"It might look nice in some colourwork."
"It might look nice if it had some colour. So might some of the cotton if you had soaked it thoroughly before dyeing and left it in the pot overnight, instead of rushing about, too cocky by half."
"Hmm, well, I suppose."
I gathered up the fabric and turned to go indoors.
Elinor called after me.
"Let's say, one kilogramme of birch bark could dye one kilogramme of fibres. If you did it properly."