Although walnut hulls are often the dye of choice for browns, I decided to use oak leaves and acorns in my tests, because the walnut tree is not native to Britain and walnuts may not have been widely available during the early Anglo-Saxon period. I harvested the acorns and oak leaves in early Autumn and dried the leaves before use. As oak leaves and acorns are rich in tannin, no mordant is needed.
The first photo below shows colours from oak leaves. An alum or clubmoss mordant produced slightly more yellowish colours and a tannin mordant made the colours deeper. An alkaline modifier increased the depth of these colours. Mid-grey was achieved on unmordanted fibres modified in iron and a very dark grey was achieved on tannin-mordanted fibres modified in iron.
The second photo below shows colours from acorns. The comments on mordants and modifiers, made above for oak leaves, also apply to acorns. The dark grey was achieved on tannin-mordanted fibres modified in iron.