Re: [ATM] Polishing staining

[Dominic-Luc Webb <dlwebb@canit.se>]

On Fri, 18 Jan 2008, Bob May wrote:

> Organics would also explain why I don't see the problem if I
> don't allow the mirror to dry before washing it of the CeO.  That
> could also explain why I sometimes see laps go "dead" and not
> polish the glass after a while, another problem that I've seen
> when polishing.  Resurfacing the lap, either by making a new lap
> or scraping the surface throughly seems to fix that problem for a
> while.  There are times when the muni water is so bad that you
> don't even want to smell it, much less drink it without boiling
> it.  A very hard water is normal around Southern Calif.


Nice to have you on board on this issue Bob! It was never much
speculation to me. It was just simple fact. Why pitch would
behave this way probably has much to do with the organic
composition of pitch. It is apparently a mixture of different
organics of different water solubilities, although they are
all technically water insoluble. I have heated Gugolz in water,
below boiling, and it is immediately clear there are substances
that come out from the pitch and remain partially dispersed in
the water phase, but the main clump of pitch never dissolves, even
if it is a very small clump in a large volume of water. It is
well known that hydrophobic organics in water can readily adhere
to glass, and can be a real challenge to remove. Perhaps this
partially water soluble substance that can readily transfer to
the glass (speculation).

The original poster used acetone, finding it seemed to work
better than thinner (mineral). These are both organic solvents,
but somewhat different classes (acetone being weak/medium polar
aprotic), so it should not be a surprise if one works better
than another. It would be nice to check through the entire
spectrum of solvent classes. I would think acid alcohol would
work well here. The most obvious choice must be 50% each of
ethanol and dilute (1:10?) HCl, the latter often sold for
swimming pools. There should be a chemical approach that will
remove this very effectively, and I suspect it can be done
without resorting to the more dangerous organic solvents.

Taking it the other way around, you could try some base-driven
hydrolysis reactions with KOH (potassium hydroxide). This
sometimes works as a saponifier, etc. NaOH is a bit more common
as it is sold as oven cleaner, but KOH is more soluble in
organics and would probably be more effective. You can always
add some oven cleaner and see what happens. If that works, KOH
might just work even better.

Dominic

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