I have two solar ovens which I made at my daughters school, (more information here, https://spidersworkshop.wordpress.com/2011/03/25/cooking-with-the-sun/). In the summer I use them for cooking, but when the sun isn’t very strong they are perfect for dyeing yarn and wool.
The solar oven is basically a box with a door at the back. All of the walls and floor are made with two walls, with a space of 5cm between that is filled with scrunched up newspaper. This insulates the oven. The glass “roof” is a form of double glazing, (two pieces of glass glued together at the edges, forming a pocket of air between them). There are also mirrors inside the oven to concentrate the sunlight.
There are many different types of solar ovens and some designs work better in different parts of the world depending on the angle of the sun and the time of the year you wish to use it. Before I had a solar oven I dyed yarn using the same principles but inside a black plastic box. I am sure anyone who does not have access to an oven can experiment with insulated boxes and other materials.
To start the dyeing I soak the clean yarn in cold water while I collect the leaves I am going to use for dying. With the white wool I put onion skins in one jar and ivy leaves in a second jar. I place the yarn into the two jars and fill them with cold water and a tablespoonful of vinegar.
I have learned that if the water is not level between the two jars the water will move through the yarn to make them even, taking the dye with it. This can make interesting effects.
I place the jars in the oven and close the door. If the sun is very strong I will have to watch them more carefully, but this week the sun has not been strong, so I just left the jars alone.
I particular like working with onion skins and watching how different colours creep up above the dye line. I left this yarn for two days then took the yarn out and washed it. I then put a dark grey yarn in with the same onion skins but changed the ivy leaves for pear leaves.
I left this wool for two days as well. After washing and drying this is what I am left with.
Near the orange from the onion skins there is a pale pink which was above the dye line.
I also have a pot with a glass lid which I use for larger batches. Wool or yarn can also be painted and wrapped in plastic food wrap and put in the oven. Similar to dyeing with steam or in a microwave oven, only this takes longer.
The advantages in using sun is it is a free energy and it works slowly, heating the wool up gently. My ovens can’t boil water, so I know the temperatures will be hot but without the agitation of boiling.
Please fell free to ask questions if there is any thing I have missed or your own experiences and tips for dying fibre!