I suspect I am not alone in sometimes finding it difficult to achieve a really deep brown from walnut hulls. However, one solution to this problem is to use fresh green walnut hulls, rather than dried brown ones. This Autumn I was lucky enough to harvest some walnuts and, after eating the nuts, I saved the green hulls to use for dyeing. I left the hulls until they had started to become brown before I simmered them until the liquid was deep brown in colour. I then strained off the liquid, added some unmordanted wool skeins and simmered them for about an hour. I left them to steep in the cooling dyebath overnight before rinsing and washing them.
As can be seen from the first two skeins in the photo below, this dyebath gave a rich deep brown and the exhaust dyebath gave a paler shade. Now I just have to find a reliable source of fresh walnuts each year. However, I should be able to use these hulls for a year or two, as I always save the used hulls, plus their liquid, to use again and again. Don’t worry if mould forms as time passes – this will only improve the dye.