[ATM] Parabolization Progress on Mirror Face? Please Help?

[Bryan Stiles <bryan.stiles@gmail.com>]

Good Morning Everyone, I have a newbie question (again). I am working
on my first mirror (8" f/6) and have just begun the figuring stroke
with the MOT. I am using a pretty thin CeO mix. Contact seems very
good and there is a nice smooth friction to the movements.

Trying to sneak up on the correct figure, I worked about ten minutes
and removed the mirror to see where I was. I placed the mirror on the
(foucault) test stand and had a look. What I saw was a small bump
(1.5"-2" dia) in the middle of the mirror. The remaining surface
seemed to be left at the sphere (since it darkened evenly at the ROC).

After seeing that I wondered what was going on? So I warm-pressed and
began working again MOT (after everything cooled down). Another
ten-fifteen minutes of work and had another look. The bump was larger
(2.5"-3.5" dia).

Afraid of what I might be doing to my mirror, I stopped for the night
to let everything cool down and ask for help in figuring this all out.

After looking at the mirror this morning, the image is the same. I
switched over to a grating and had a look inside and outside of ROC.
The image seemed to indicate that the bump is a something different
(parabola?) than the remaining surface. The lines on the remaining
surface stay nice and straight while moving back and forth.
Conversely, the lines on the bump bow and roll with movement.


The theory that I'm working with is that the bump is actually the
progress of parabolization moving out to the edge of the mirror. That
leaves the remaining surface as a sphere.

I would sincerely appreciate any guidance you could provide. 

Bryan Stiles
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