Hi Colin,
I have some experience in using dry pigments with PU resin, but the principle should be the same for epoxy. I'm using some synthetic pigments from Kremer, and they results are stunning.
Anyway, here is how I do it.
I add approx. 2% pigments by weight. This gives very strong saturated colors.
As Matt already told, you cannot just add dry pigments, so you have to make a paste first.
- Scoop up a sufficient amount of pigment in a small mixing cup. Make sure it has an even bottom since you need to scrape and mix quite a lot. and any dry leftovers in the groves at the bottom of a normal plastic cup will be very difficult to wet out.
- Add a very small amount of resin (not hardener).
- Start mixing and add more resin or pigment until you get a paste. It's a bit like mixing sugar glazing.
- Keep mixing the paste, making sure to squash out any remaining dry pigment. It may be a good idea to transfer the paste to a new mixing cup.
Now you can add this paste to your resin. It should be quite easy to mix, but it's a good idea to mix this in before you add hardener in case you need to spend some time with it. Again, if you can't get the mix to be even, or you get some residue on the bottom or on the sides of the mixing cup, pour the resin into a new cup (just remember to adjust for the resin you lose).
That's it. It sound like a lot of hassle, but it's really quite easy.
Kjell