Greg Granville writes :
C I finally discovered that my lap was to hard, and that I had to apply C excessive pressure to deepen the center (and then, it went way to far C all at once) C I put a few tablespoons of turpentine in my pitch bucket and poured a new C lap. Once I got it softened up a bit, I was no longer punching massive C holes in the center of the glass.
???? It is pitch which is TOO SOFT, that will get you hyperbolic shape (AND turned down edge, at no extra cost !). Hard pitch usually manifest itself as producing ripply surface, and scratches and sleeks, but general surface always stays close to sphere. (with normal strokes, of course) Maybe you haven't formed the tool properly, so it was contacting only in the center ?
C The pitch I'm using was a hand-me-down from another ATM. It's been used to C make at least three mirrors - and probably twice that number of laps. C C I'm not really sure it the stuff becomes unuseable eventually or not. ???
Yes, it gradually becomes less usefull. The turpentine is only fair substitute for complex natural solvents found in good pitch (they will eventually evaporate for good). How many times before that happens ? Beats me, I've never recycled more than few times ...
Bratislav