a former sister-in-law used to 'borrow' the walnuts we grew (before the trunk got hollow and we had to cut it down). She scoured the 'velvet' off the outside and gave me back the scrubbed nuts (ooh, Matron) which I could then leave on the boiler in a basket for a few months before munching them at Christmas.
What she did with all the yucky velvet scrapings was to steep them in water then boil it up and reduce down, ending up with a cream-consistency gunge which she used for single colour watercolour paintings - different dilutions giving the sepia equivalent of grey scale.
Odd woman. Talented artist but daft as a box of frogs.
