Some years I wouldn't bother with acorns as a dye material because the English Oaks don't always produce much of a crop. This year has been fairly good, and the acorns have been lying thickly on the ground in places so it made sense to scoop them up into my pocket whilst walking.
We have a couple of different species of oak in the UK mainland and Northern Ireland. The oak is our great traditional tree. Most stately homes across the British Isles and Ireland, will have a few ancient oaks. I have seen some that are said to be 800 years old. This one below is at the back of my house, it's just a young tree and the leaves are now dropping every day.
All parts of the oak tree are useful for dyeing with. Colours from leaves and bark range from buff to a mustard- brown/greeny - brown. Colours from the galls range from light to dark grey, and from the acorns they are in the mustard brown -to grey range. Technically you don't need to pre-mordant the fibre before dyeing because of the tannin, but in this instance, I have used pre-mordanted white Shetland tops, mordant used was alum.
I weighed out 1.7 kilos of dried acorns. That is actually more than is shown in the above picture, only my container wouldn't hold them all. I don't often follow a 'recipe' for natural plant dyeing but a rule of thumb for many dye plants is at least twice the weight of dye material to fibre. In this case I was way over that. I used 1.7 kilos to dye 200grams of fibre, so that was 8x weight of dye material to fibre. I do this kind of ratio quite often because I like to really get bold colours. There's nothing worse than going through all this work only to end up with such a pale buff colour you are hard pressed to know if it actually is dyed or not. I would get a good depth of colour on the first dyeing and use the waste dye bath that the fibre doesn't take up to dye a second lighter batch.
So, into my very large stainless steel pot the acorns went, and I covered with soft water for a couple of days. Usually I would crush them with a mallet and then add them to the water, but because they were dried, they were very hard, so my crushing of them had to be done after soaking.
After a few days soaking, and a rough crush with the mallet, I simmered this pot for about 3 hours, very slowly over a low heat. This initial boiling is only in a few inches of water. The amount of water doesn't matter too much. Then I strained off the acorns, and re-simmered them in fresh water to extract more dye. I repeated this twice more until the water was coming clear. I do this with most natural dye plants, re-simmering to extract the last drop of colour. After they were completely exhausted of colour I added them to the compost heap.
Below is a photo of some white Shetland tops being added to the dye bath. Usually it is best to soak the fibre before adding to the bath, but in this instance it made not a scrap of difference. I planned to soak it over night before adding any heat, and the fibre took up the water very readily. Before simmering, I made sure the fibre was all evenly soaked and then I simmered it low for about an hour.
I always find the next bit a wee bit tricky because although the colour of the fibre was dyed a nice chestnut colour, I wanted more depth, and something in the greeny/greyer shades. The recognised method of getting dark grey, is to add iron.
I'm not wildly enthusiastic about using iron on wool because it is harsh. Last time I dyed with acorns I added a whole teaspoon of dissolved iron to the dye bath and got a really good deep grey, but this time I decided to use less iron.
This quarter teaspoon was exactly what I used. This is being added to about a gallon of fluid in the dye pot. It's tricky because after dissolving the iron (use gloves and mask and dispose of spent fluids responsibly) in very hot water in a jam-jar, it needs to be added to the dye bath without messing up the fibre. You don't want to dump the concentrated iron solution straight onto fibre. As fibre can easily felt in a dye bath, I don't lift the fibre out, but instead I have a large scoop that I push the fibre to one side of the dye-pot with, and then gradually add the iron, mixing all the fluid in bit by bit before releasing the fibre back onto that side of the pot.
I've taken the pot off the stove top each time and photographed outside to show true colours. The whole dye pot turns a dramatic inky dark brown - black when the iron is added. A further simmering of no more than 7 or 8 minutes has completed the process for me. I could have added more iron, I could simmer for longer, but I'm very cautious about damaging fibre, and I was really pleased with this colour, so I stopped there.
Another word of caution; the dye colour in the pot when the fibre is still wet is a darker colour from when it is rinsed and dried, as the photos below demonstrate. Bear that in mind when you make your decisions about how long to simmer and how much iron to add. If you have to lift the fibre out, and rinse, and then return it to the pot to obtain more depth of colour, the manipulation of the fibre increases the risk of felting, so it's best to make a decision and stick with it.
Photos taken on a very dull wet November day, one against a dark background, the other against white. Not sure either of these pics truly represent the colour I obtained, but hopefully they help.
'Its only grey- brown' I hear someone say. Yes, it is, but with green under-tones, and a valuable additional colour for truly authentic Shetland and Norwegian knitting.