Reply To: Epoxy dye
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I make surfboards as a hobby, and I’ve tinted and pigmented epoxies for about 30-40 epoxy surfboards. You can buy special tints (leaves the epoxy still a bit see-through) or pigments (opaque) that are intended for use with surfboard resins, be it epoxy or polyester resin.
FWIW, if you are going to be using lots of epoxy where it can be seen, and want the piece to look nice for decades, use a surfboard-specific epoxy, because they contain UV-inhibiting agents. Most normal epoxies, even high-quality ones like West Systems, will yellow in just a couple of years. Not a good look. The epoxy is still super strong, but it looks bad. So something like Resin Research (http://shop.fiberglasssupply.com/Epoxy-Resin_Research_Epoxy.html) will resist yellowing for many years to come.
But yellowing is much less of an issue if you’re going to make your epoxy pitch black with a heavy opaque pigment. Here are some colors: http://www.foamez.com/glassing-surfboards-surfboard-pigments-tints-c-3_34.html. Keep in mind the opaque pigments like black, dark blue, red, etc need very, very little product to go full opaque. 2 oz of black pigment will blacken at least a gallon, maybe 2 or 3, of epoxy. Tints are a different animal, and require skill and practice for a perfectly even and predictable result, so consider avoiding them unless you’re willing to practice on quite a few test batches first.
Having said all that, epoxy can generally tolerate being pigmented by other things besides resin-specific tints and pigments (tints are still another animal). However, if you are going to use some scary old paint you have lying around from the Korean war era, just mix up a test batch first — there are some things that will have less-than-favorable interactions with the resin curing process. So mix up a test batch, let it cure for a few days, and make sure the result is still reasonably hard and strong. If it cured hard, you’re probably GTG.