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Re: [ATM] A very rough surface mirror
Francis:
While I can't give you an exact equation for what happened to me many years
ago, it went something like this; concentrated room temperature NaOH
standing on the surface for an hour or two failed to remove ALL of the old
coating, so remembering from high school chemistry that HEAT often speeds
things up where chemistry is concerned, I mixed up a new batch of fresh NaOH
in water that was uncomfortably hot to touch and let that mixture stand
overnight on the surface of my beautifully figured, smooth paraboloid. Next
morning I returned to claim the fruits of my labor and found the glass so
badly etched that I could no longer see through it (but hey, NONE of that
pesky aluminum was left either)...
A less extreme example a year or two later did not result in total fatality,
however, increased scatter could be seen under a careful knife-edge test
after a (much shorter duration) NaOH strip; that was enough for me, and I
now steer clear from using this stuff on Pyrex. It may still have a place
stripping coatings off of pure silica or Zerodur, but I haven't tried any
experiments there myself.
Equations: NaOH + your love object = ARRRRGHHHH!!!!!
Scott M
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Francis J. O'Reilly
Sent: Sunday, October 21, 2007 9:52 AM
To: Dale Eason; atm@atmlist.net
Subject: Re: [ATM] A very rough surface mirror
Dale,
I would think that it was the result of a very hard lap, too fast stroke and
very poor pitch lap to mirror contact. That being said, with a new lap of
good quality, use 1 tablespoon of aluminum hydroxide oxide to one quart of
water for about an hour then rinse throughly, (Note, this I politely
disagree with Guy on this matter) to clean the rest of the aluminum coating
followed by half an hour of tool on top followed by half an hour of mirror
on top, and the mirror should be pretty close to returning to a sphere.
As to Guy's asertion that a caustic bath is injurious to a mirror's figure,
My experience is counter to his assertion. I would however prefer to
continue this debate using conclusions drawn from the sciences, rather than
our bare assertions that it does or does not affect the figure. Can anyone
offer if not chemical equations, at least an explanation as to why this may
or may not be?
Thank you all.
Francis J. O'Reilly
----- Original Message -----
From: "Dale Eason" <atmpob@yahoo.com>
To: <atm@atmlist.net>
Sent: Saturday, October 20, 2007 10:33 PM
Subject: [ATM] A very rough surface mirror
> http://home.comcast.net/~doeason/Surface_images.pdf
> 1meg file.
>
> This mirror has a surface similar to one that Texereau
> shows in his book where he states it was caused by too
> much pressure and too fast a stroke by an over
> enthusiastic mirror maker.
>
> This is about the worst surface I have ever measured.
> I am using the PDF file format because there is a lot
> of detail in these images and one can zoom in and out
> of them easily in that format. I show real ronchi and
> Foucault images and compare them to the
> interferometric data.
>
> Would anyone care to speculate on the cause of this
> surface? The mirror is an 8 molded Pyrex blank. The
> the words "Pyrex made in the USA" and "8D" molded
> into the back. The sides are slightly tapered to
> allow it to be removed from the mold. It was once
> aluminum coated but nearly all of it has gone.
>
>
> Dale Eason
>
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