Does anyone know of a fill (epoxy, etc.) that can be used to fill checks? Black would be fine.
From contributor D:
You probably already know this trick, but just in case, for a minor job just go to the HD and get some five min epoxy, sand the heck out of your walnut and make a ton of fine sawdust. Mask off the areas around the checks with tape. Mix the dust and epoxy, thick enough to have lots of color but not so thin that itís plastic like when dry. Then fill the checks with the mix using a thin putty type knife or thin flat off-cut (I like the flexibility). Don't use too much, once dry it's a pain to knock down.
I actually use a plane or scraper to get the bulk off then go to sanding. I have done this trick a few times and applied finish over with excellent results. The finish will absorb if you get the mix right. For bigger jobs you can try marine epoxy, but you'll need to make a lot of sawdust.