...on black ash cabinets. Any tried and tested ideas? I've read black shoe polish, even crayons rubbed over the offending area.
Depends on the finish, is it real wood veneer? I would not use canyons as that will show in reflected light, polish may work. They are wood restoring products around or wood staining?
I have used shoe polish on black furniture. It is certainly an improvement, costs virtually nothing and is easy to do.