Re: [ATM] Life on the edge

[Ben McIlwain <cydeweys@gmail.com>]

ArtfulBodger wrote:
> Hey there, boys & girls.  This is sort of a mundane question, but 
> it's bugging me, so I'll ask.
> 
> I'm making my first mirror, Pyrex, 10", and it's coming out well. 
> I've polished with cerium oxide and then "super cerium," which I'm 
> told has a smaller grain size.  The mirror surface is pretty: it 
> looks well, tests well, and I'm just about to start figuring.
> 
> But here's the thing: I can't get the edge clean.  The cerium -- 
> regular or super -- sticks better than paint.  I guess there's no 
> reason why the edge has to be all sparkly bright; I just want it to be.
> 
> Before grinding, I cleaned up the cast blank with a diamond bench 
> stone.  I have a couple of grades of these for tool sharpening, and 
> they did well on the glass: it's transparent but slightly fogged. 
> I've left the back and edge this way and haven't polished them.
> 
> The cerium slurry drools over the edge and stays there, and however 
> hard I scrub, the white stains remain.  So.  Hmm.  The diamond hone 
> would clean things up fine, but I'm not going anywhere near that 
> mirror with a diamond abrasive.
> 
> Somebody told me I should use cratex or a great big eraser.  That 
> sounded good, but it didn't work.  I have a bunch of art & drafting 
> erasers around here, but none of them could touch the cerium.
> 
> I thought maybe I could put some of the polishing slurry on a tile, 
> and go around the edge with that: fight cerium with cerium.  Pretty 
> sure that would do it, though I'd have to be careful not to mar the 
> mirror surface.
> 
> Or is there a simpler way I'm overlooking?  Or should I just not 
> bother?  I'll appreciate your suggestions.

Definitely not bother.  As long as it's just on the edge and not on the
mirror surface itself, it won't be a problem.  If it won't come off
after vigorous rubbing with water and paper towels then it's not going
to come off in normal conditions.  Just remember what you're making - a
mirror that's going to go inside a long tube.  You're never going to see
the edges again after you assemble your scope, and it truly won't
matter.  It's best not to risk doing any damage to your finely polished
mirror surface by attempting to clean up an inconsequential edge.

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