The photo below shows my new lap, poured from straight Gugholz 64. My lack of experience caused me to let it cool a bit too much before I attempted to channel it, so I was in an awful hurry to get that done before the pitch got too hard. Hence, perhaps, the uneven facet sizes, although I hope that's not a problem. The lap is also thicker than necessary, and the channels only go down about half the pitch thickness. I may deepen them before I attempt again to parabolize.
A couple of sessions of 1/3 center-over-center strokes have not made a noticeable difference in the ring zones visible in the photos in the last post. They have, however, produced some overall roughness. I guess, barring contrary advice, I'll just go ahead and do some more of the same. The same stroke, with constant around-the-barrel walking and mirror rotation, produced a nice smooth sphere prior to my first attempt to parabolize.