From: Mark Holm 
To: atm{at}shore.net
Reply-To: Mark Holm 


> This comes up every once in a while on the list, but that might be a good =
> thing.  I don't know how long it would take a hydroxide solution to etch =
> an optical surface enough to cause an optical effect.   I know others have =
> used hydroxide to remove coatings and said there was no effect on figure. =
> However, I assume roughness would be the more likely result, and no one =
> has ever said they looked at roughness after using hydroxide.  I consider =
> that an open question.  Anyone have data?
>
>
I think it is in the very last issue of ATMJ, issue 17?  There is an article on

phase contrast testing, a method that lets you see small surface details. 
As I recall,

there are pictures showing damage from a caustic solution.  It is small,
but definitely there.  The glass roughened noticeably.  If you can see it
with an optical test, then it must affect imaging.  Given the nature of the
phase contrast test, the natural conclusion is that the roughness scatters
light at a rather large angle from it's proper place, much larger than just
throwing it into the first couple of diffraction rings.  The effect would
probably be similar to a ground glass except that much less light is
scattered.

I have seen glass that was severely etched by caustic.  That is like ground glass!

Mark Holm
mdholm{at}telerama.com

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