[ATM] Phase Contrast and Foucault image puzzle

[Mel Bartels]

> Has anyone any idea what has caused the groves and
> winding features seen in the Foucault image?  None of
> the features visible on the back show up in Foucault
> image.


I've never seen it so striking.  I've seen heavy polishing that makes the
glass look like frozen waves and I've seen horribly overpowering cleaning by
harsh acids that etch the glass.  The circular strokes centered on center
make me suspicious of the latter.

Mel Bartels