Re: [ATM] ATM: pitch removal

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

The Alarm Co. wrote:
> A kind benefactor bequeathed me a 10" f/3.5 (approximately) mirror cored
> almost through for a Cassegrain, along with an assortment of grits and other
> 'scope stuff.  I plan to finish the scope, but first I need to clean the
> mirror to test it and see what I have.  The face of the mirror has what
> appears to be pitch bonded to it in a pattern reminiscent of bubble wrap or
> the suction cups on the bottom of some shower mats.  I say "appears" because
> it doesn't look like the Gugolz I use.  It is much lighter in color, almost
> orange.  Is it perhaps burgundy pitch?  What's the best way to remove
> this gunk without damaging the mirror?

Sounds like some burgundy pitch, something like the stuff from 
Willmann-Bell.  Orangish-tan color.

If it were me and it is Pyrex, I'd put the mirror in the freezer for a 
few hours.  The pitch will be very brittle after this.  Then get it 
out and if the pitch on the face is not that thick, it should pop off 
using your fingernail or the handle of a plastic fork, or something 
made of plastic (which won't scratch if it touches the face of the 
mirror).  Rapping with your knuckles might even knock it off.  A block 
of wood might work for gently tapping or striking the pitch to break 
it off.  (Make sure the wood is free of dirt, etc.)

WARNING:  Be VERY careful when tapping on the mirror near the center 
core.  It could easily be dislodged (broken) if you hit it.  Take your 
time and scratch away the pitch there little by little with your 
fingernail or the fork (or a plastic knife).

Then simply remove the residue by wiping with turpentine and a clean 
cloth or paper towel.

	Mike Lockwood


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