System Three says that no pigment or filler provides adequate UV protection.
The UV will break down the outer layers first, and depending on which filler
and how densely it was added, the UV will penetrate further too. The joint
(below) is protected from UV by the wood. Best idea for epoxy coatings is
to add a UV coating on the outside. And even with that, if it's a clear
coat then the UV inhibitors do get used up and the clear coat itself needs
renewing now and then. Paint or gelcoat is better.

Brian


"Dave W" wrote in message
...
I don't know about the degree of UV protection offered by tinting. In
terms of how dark can one tint, I have added black color to make the epoxy
as dark as ebony. By the way, I have had a test sample of epoxy and
fiberglass scarfed plywood in the bed of my truck for four years with no
apparent loss in strength of the joint. The (clear) epoxy has yellowed a
bit but the joint seems to be very strong.
Dave