Cleaning Aluminized Telescope Mirrors
Big mirrors seem to have a fatal attraction to kitchen sinks.
Mirrors are much happier on their back on the lawn, just watch out for the reflection of the sun.
Forget about that lens cleaning kit with the little bottles of stuff. That won't do this job.
Other things that won't work, vinegar, silver polish, and no, never use cleanser or similar.
We will presume this mirror has been in a flood or a tornado and is covered with grit glued down with plant resins.
So water spray alone will take some of the large grit away.
Note, yes this mirror is not coated but it was available at the moment.
If the mirror edge is sharp there is almost 100 percent chance that it will get flake type chips eventually.
If the mirror will need to be re-coated that is a good time to dull the edge with a wood block and
120 grit alumina sand paper. Be sure to get rid of all grit before wrapping.
The significant items in this picture are two pans of almost too hot water, dish washing detergent, paper towels and semiconductor grade 10 methyl alcohol warmed in the sun. And no slip shoes and be very careful.
70 percent rubbing alcohol
some types of toilet paper
Put a bit of dish washing liquid in one pan and soak the paper towel until soft.
Wipe the mirror lightly, don't press down.
Move to the rinse pan. That was easy, now the hard part.
Carefully remove the mirror from the pan and pour alcohol over it to get rid of the water.
Tip the mirror up to get rid of excess alcohol. A bit of pre planning helps.
Before the drops of alcohol can dry drag a dry towel sheet across the mirror to spread out the alcohol.
Don't press down while dragging the towel.
Then put the mirror in a safe place and lay a dry paper towel on it and take a break.
The mirror's coating becomes much harder after several years making the cleaning process easier.
Sky and Telescope March 2019 issue has a good article on mirror care.
Among other good suggestions they recommend using cotton balls for swabbing the mirror.
And they recommend using only one light sweep per cotton ball to avoid scratching the
coating with grit accumulated on the cotton ball.
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Other cleaning procedures worth mentioning. ( I have never used these procedures . ) Cleaning with Collodion
Collodion is poured on the mirror and as it dries it shrinks and separates taking the dust with it.
For instructions refer to a PAS members web-site.
People who should know have told me that some observatory mirrors have been cleaned
using carbon dioxide snow. ( As in CO2 fire extinguisher. )
I have never seen this done but I can predict at least two problems.
The cold CO2 will condense lots of water out of the air.
The cold shock might cause green glass mirrors to crack in half.
( Never put a green glass mirror blank in a pan of cold water in the sun.)
If CO2 cleaning might be appropriate for your project try the link: http://www.co2clean.com/