Recently I conducted some experiments with fresh, dried and frozen walnut hulls, to see if there was any difference in the colour achieved from each. Using fresh green walnuts kindly donated by Deborah Barker and all collected at the same time from the same tree, some were put in the freezer immediately, some left to dry out and some used fresh from the tree. I used whole walnuts as this was easier than trying to separate the outer shell from the nut. The frozen and dried walnuts became dark brown and the fresh walnuts also appeared dark brown when I put them in the dye bath.
Fresh green walnuts
I put 2 walnuts in each of 3 containers, added samples of wool, silk and linen (no mordant) to each container and then added hot water. I decided to experiment with dyeing without further heat, so I put a lid on each of the containers and left them for about 4 weeks. I checked from time to time and stirred gently.
The results were interesting. There was little difference between the shades from each dye bath, although the results from the dye bath made with fresh walnuts seemed a little paler. I had expected the fresh walnuts to give the deepest shades and the dried walnuts the palest but strangely enough the results were the reverse, with the dried walnuts appearing to give slightly deeper shades. In all cases the colours were deeper than I usually get from dried walnuts. I assume that the fresh walnuts may not have given deeper shades because they were no longer fresh and green when the dye bath was made.
In my experience, the best way to get deep browns if using dried walnuts is to add clear vinegar to the dye bath to pH4.5. This I learned from Helen Melvin and I have found it particularly effective on wool and silk.
Walnut hulls on linen and silk fabric and wool yarn (no mordant)
Top: fresh walnut hulls
Below left: Frozen walnut hulls Below right: Dried walnut hulls