OP
The castings are indeed solid. I actually do quite a bit of grinding on the "inside" of each adapter after it comes out of the mold, to get rid of the sprue and the residue of the parting lines. When just out of the mold the material is soft enough to carve with sharp knives, but within a half hour I have to shift to a small milling cutter in a flexible shaft tool.
You certainly can grind or sand on the face of the adapter as well, and the entire pour is tinted so the color is consistent throughout the part. But be aware of a couple of things: First, the resin often releases lots of very tiny bubbles as it sets up in the mold. These bubbles generally stay away from the surface of the mold, which is why I get a smooth working surface (I suspect that the outer surface of the part starts to set up before the bubbles begin to form.) But "inside" you are likely to run into them pretty much everywhere, and when you do they will give you a non-smooth surface anywhere you expose one of 'em. You can sand your new surface smooth, but the sanding dust (which will be white) will fill in the tiny pores these bubbles will leave, and you'll have a speckled surface to look at. It may be so smooth that you won't really feel the pores, but it probably won't look very good.
And second, I haven't found anything yet that lets me polish this stuff as smooth as it comes out of the mold. So if you carve away at the face of the adapter, you may not be able to get even the solid areas back to as smooth a surface as you started from.
I have spoken with my materials supplier and they say that the bubbles that form during setup are just part of the chemical process going on during the cure. The particular material that I use is designed to be tinted, so the fact that it may contain internal bubbles when hard isn't a real concern. I would use other materials if I needed crystal clear parts, but those materials don't lend themselves to coloring as well as what I use.
