Ever tried the Onyx resin before? I've grown to be a big fan of it, really great properties for slushing and the fast cure version shaves a lot of cure time off for much faster production. Higher melting temp makes it much more warp resistant too. And if you choose to offer cold-casts of these the black naturally helps that too. Only problem is it's hardness can make it brittle when thin, but looks like you're casting these very thickly.