I checked on Acraglas yesterday, and it would cost me almost $40 for the smallest 4 oz kit that I would need less than a quarter teaspoon of. I asked my local gunsmith and he said for such work he uses slow cure epoxy. What kind of dyes will mix with epoxy? I assume things like brown shoe polish and common oil stains are incompatible. Maybe the fill area is so narrow that I would need no colorant at all?