I've had both good and bad luck tinting epoxy. I think it depends on the particular brand of glue. With some "5-minute" brands I have had good luck using Testor's flat black or brown model enamel (used a lot of the florescent colors to tint pistol sight inserts too.) I've also used acrylic artists colors. One kind of glue refused to set with acrylic, though. Try different brands of glue before giving up on any particular coloring agent, as some seem to be more compatible than others. If the repair sets only to a 'rubbery' consistency, you may get a harder set by using excess hardener in the epoxy mix.Brownell's dyes are good, especially when used with their brand of Acraglas epoxy, but are a bit pricey and you can't get them at the local shop and drop...
Ken Houston (gunhou)
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The sword cannot cut itself, the eye cannot see itself.