From: krod@cbnewsd.cb.att.com (craig.engelhorn)
Subject: Re: Cleaning mirrors
Organization: AT&T
Date: Tue, 26 Jan 1993 21:23:46 GMT



Cleaning aluminized optical surfaces is a tricky business.  If you are careful,
it can be done safely with minimal risk to your delicate surfaces.
Since there is risk of damage to the surface every time you clean, 
don't rush to clean the optics just because one or two chunks of dust appear.

The best advice is to store your telescope in such a way that dust may not fall
on the surface.  Cover the tube.  Texereau suggests storing the mirror upside
down so the "heavier, greasier" particles don't land on the surface at all.
In any case, crud will accumulate and you will need to clean the optics to 
insure the best performance.

You will need.  
	A squeeze bulb, or compressed air can.
	Distilled water
	Detergent
	Cotton balls

This is the technique I use, borrowed from an article in Astronomy Magazine
March 1992 by Micheal Porcellino.

1> Take the mirror out of the telescope.  Careful.  Mark the mirror edge so you
	can replace it into the cell the same way it was before.

2> Use the can of compressed air (don't agitate it before use), or the squeeze
	bulb to blow off the big chunks.  (Sounds like you have gone this far)
	Do not use a brush, and never drag anything dry across the mirror
	surface.

3> Use wet cotton balls to "lift" off any remaining large chunks.  Do not wipe.
	Lift.  Do not use pressure, just snag the chunks with cotton balls
	and lift them off.  Use plenty of cotton balls, don't continue to use
	the same one over and over, it could pick up a really nasty chunk and
	scratch your surface.

4> Wash the mirror in room temperature tap water.  Gently.  
	First, clean and rinse the sink.
	Line the sink with a folded towel. 
	Gently flow room temperature water over the surface.

5> Rinse the mirror with distilled water.  Let it dry standing on edge.
	Again, blot the surface with wet cotton balls to lift dirt.

6> Fill up a clean sink with water and detergent and soak the mirror for a few 
	minutes.  The water and mirror should both be room temp.  Line the sink
	bottom with a lint free towel.  We don't want to break a mirror dropped
	onto a hard sink bottom, or fracture it with hot or cold water.

7> Swirl the mirror under the water to wash the surface.

8> GENTLY wipe the surface with cotton balls as  the mirror is submerged. 
	Swab using a straight motion from one edge to the other.
	Use only the weight of the cotton, and pitch the cotton balls after each	pass.
	Make as few passes as possible.  Do not repeatedly go over the mirror.

9> Drain the sink, and rinse with lots of tap water.

10> Rinse again with plenty of distilled water, and set it on edge to dry.  
	Carefully. 

Bottom line, be careful, and there's going to be no problem.
Personally, it scares the hell out of me just to handle my mirrors, let alone
clean them.  I figure every time I hold my mirror I am increasing the chance
that it will get dropped.  

I dropped a 6 inch mirror onto concrete just after I had finished the fine
grinding stage.  It was wrapped in a towel and did NOT break or chip. I was
lucky.


Craig Engelhorn
AT&T Bell Laboratories
cae@iexist.att.com
Newsgroups: sci.astro