: I've used toner to blacken epoxy for years. I used it because it was there.
: If I had a choice given to me I'd use the graphite. It takes extremely
: little to blacken epoxy -like a quarter teaspoon to a cup. I found no
: negatives in using it and for me I used the waste toner from a copy
: machine so it was free.

I use System Three black color additive. It is a liquid (thin paste). It take a very small amount to change clear epoxy jet black.

Larry C.