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Re: Deposits on Glass

Hi all,
I looked through the archives to see what was said back then...around Jan
98, and all I did was get more confused!  These are the points some people

-SiO2 is generally not soluble in water, thus...
-SiO2 "deposits" wouldn't be made in the same manner as Ca, but...
-recurring evaporation at the water line can dissolve and redeposit SiO2 to
form rings
-these "deposits" are not affected by vinegar, muriatic, or even 100% HCl acid
-they can be removed by hydrofluoric acid and telescope polishing paper,
with consequence

Dave, do you disagree with the above points?  I hope you or someone
disagrees!  I hope these SiO2 deposits aren't actually *etchings* in my
glass...I hope they are something like deposits made on top of the glass!
If the glass itself did indeed disolve and redeposit, I would only have two
options (that I know of) to clean the tank:  hydrofluoric acid, and
telescope polishing paper.  I don't know if the hydrofluoric acid would
work...if it dissolved the SiO2 rings, what would keep it from dissolving
the SiO2 tank?  Beside, another post in the archives said hydrofluoric acid
created a spotted surface.  And the telescope polishing paper would created
dips in the glass of the tank, so it would be "smooth" but "curved".  As
Jean Olsen said in one post:  "You will not polish it evenly, which will
mean the surface willno longer be 'parallel,' which is another way of
saying you are polishing little lens structures into the surface....they
might make the view through that top glass slightly distorted."

There seems to be a lot of people with this problem, I hope the APD can get
it resolved!  Please help!

At 03:48 AM 9/22/98 -0400, Dave Gomberg wrote:
>OK, now THAT (erosion, etching) is credible.   I had a big fight with
>someone who will remain unnamed who also claimed SiO2 deposition and I
>refused to believe it.   If it is erosion, there are glass polishing
>compounds (used by telescope makers) that should solve the problem.  They
>have abrasives that go all the way from major glass removal to polishing to
>.1 wave should you feel so inclined.
>- --
>Dave Gomberg, San Francisco            mailto:gomberg at wcf_com
>FormMaestro                              <http://www.wcf.com>