Recently acquired a new-to-me Artisat loom. It generally seems in good shape, but a bit grubby. The heddles had a bit of rust, so replaced those, metal rod cleaned up with a bit of 3 in 1 oil and some steel wool fairly easily. The trouble is the apron. It was grey and dusty on the top of the beam it was wound round. Does not look like mildew, a pretty even coat of grey just on top. I vacuumed it and when I run a very slightly damp cloth over, nothing comes off. Am hesitant to take the apron off, it is stapled to the beam and I am not sure I could fix it back on. And hesitant to try washing it. Any advice would be great!