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Cleaning rough off Mirror being Made

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#1 JohnH

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Posted 13 October 2013 - 01:04 PM

I am getting back to my 12.5 f4.8 project and I wanted to improve the look of my mirror before doing final tests and corrections.

There is still some rough present from the polishing process and I wanted to clean it off before sending it for coating.

Tried using turpentine, paint thinner and methyl hydrate, as I thought part of the reason it stuck on so well is some pitch is mixed in with it. None of these worked and I wanted to clean it to leave the molded sides and ground bevel intact.

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#2 prfesser

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Posted 13 October 2013 - 01:22 PM

I recall a suggestion in one of the telescope-making books in which the author used a pencil eraser to remove rouge. If using this method I'd be very careful not to let the eraser slip onto the optical surface.

Best -- Prfesser

#3 JohnH

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Posted 13 October 2013 - 01:44 PM

Didn't touch it, even in the spots where there wasn't that much.

I am considering doing a silver coating as a tst on a small mirror, so I will have nitric acid around sooner or later.

#4 planet earth

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Posted 13 October 2013 - 02:19 PM

You could try warm the mirror blank up in water slowly and then use turps.
Maybe 90-110 deg F or so, to soften up the rouge /pitch.
Sam

#5 GlennLeDrew

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Posted 13 October 2013 - 03:47 PM

Acetone nicely dissolves pitch, and leaves no residue. Use it in a well ventilated area. It may not be effective on dried-on polishing compound, for which scrubbing with a nylon brush and a cleaner such as Spray Nine might be more efficacious.

#6 Jeff Phinney

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Posted 13 October 2013 - 06:48 PM

I'm assuming that the stain is not going to be visible once the mirror is mounted in the telescope.

Question: If the stain is on the side or back of the mirror and not on the face, why worry about?

#7 GlennLeDrew

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Posted 14 October 2013 - 02:31 AM

Stains should pose no problem. But I wonder about outgassing from pitch in the vacuum chamber during coating; it's safest to eliminate that.

#8 David Castillo

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Posted 14 October 2013 - 11:45 AM

You might get it off with toluene. It's an organic solvent that should dissolve that residue. It is also capable of dissolving a number of notable inorganic chemicals such as sulfur, phosphorus, bromine, and other non-polar covalent substances, so it could do the trick.If you use it be careful, it's vapor is neurotoxic if too much is inhaled. I've used it on tissue samples on slides to dissolve wax.
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#9 Don H

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Posted 14 October 2013 - 12:32 PM

Hi John. In the past I have used detergent and a soft scrub brush to clean my mirrors of rouge residue, often followed with alcohol and more soapy water. Ultimately your coater will clean your mirror to the point where I think you won't have to worry. A little left over rouge color is testament to your mirror making endeavour.

Regards,
Don

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#10 ccaissie

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Posted 20 October 2013 - 02:10 PM

Stains should pose no problem. But I wonder about outgassing from pitch in the vacuum chamber during coating; it's safest to eliminate that.


I was assured from a coater I used to use that epoxy on the back to secure a nut in a conical blank would not cause outgassing...that it was an overblown concern.

Now after a year, they still can't deliver a decent coating, so maybe he doesn't know what he's talking about. I'd say clean it up the way they used to tell you, just to be sure.

#11 Mark Harry

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Posted 21 October 2013 - 07:36 AM

I got a way.
It's called SCOTCHBRIGHT. In getting the glass polished out, I go to the sink and it cleans up the edge nicely. (just the EDGE!)
Then, I figure the mirror with a few short spells, and as soon as I lift the polisher off the glass, I spray the heck out of it with a spraybottle. This dilutes the alkaline characteristic the swarf might have, and prevents re-deposition of the crusty stuff. Then it's a total sink rinse to leave a nice pristeen optic. Works for me.
If your water is notably hard, do the rinses and sprays with distilled H2O after scrubbing the edge off.
M.

#12 JohnH

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Posted 21 October 2013 - 10:01 PM

I had forgotten that the act of grinding and polishing Pyrex results in a chemically changed material that can (and does) stain crown and flint lens blanks being worked if not rinsed promptly.






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