Gallnut

There was the smell of evening in the air, the smell of the fields in the country where they digged up turnips to peel them and eat them when they went out for a walk to Major Barton's, the smell there was in the little wood beyond the pavilion where the gallnuts were.

Source: wiktionary

[Y]our hands are always covered with gallnut [translating galla], vitriol, and alum, just like the varnish on a Moor.

Source: wiktionary