Well, I have learned two things, which will allow me to proceed.
1) I sorted through my transparent black rods and found a couple with no exterior bumps (which I take to be tiny bubbles but have no proof). These are much more well-behaved, with bubbles only at the edge, not at the surface.
2) With the ones that have bumps I experimented with gas mix. Even if I keep the rod at minimal heat the problem still exists. I then turned down the ox a bit and that had no effect. I couldn't turn it down more as it made the flame too small. So I then turned up the propane enough that the flame became slightly less efficient (slight color change) and the normal burner noise (purr) diminished to almost nothing. Bottom line, much more fuel rich than I would normally. The problem went away. I'm back to work. Shown is what I was making that was not smooth.
Further update: I sorted through my transparent black and took out all the ones rough with bubbles. Interestingly they all are the larger diameter rods that came in the order, so I think they were all one batch. I started playing with them in non-serious work but they kept shattering, again I think because of the bubbles. Moral of the story is if your rods have a rough surface that feels like someone mixed in a hundred grains of sand, they will not work.
Last edited by dwarrent; 04-25-10 at 08:58 AM.
Reason: add text