University Lowbrow Astronomers

Cleaning the 17.5 Coulter Mirror at Your Local Quarter Car Wash.

by Jack Brisbin
Printed in Reflections: April, 2008.

(This is a continuation of the article “The Odyssey 2 Continues” by Jack Brisbin, February, 2008).

You are probably wondering why anyone would clean their telescope mirror at a car wash. The water from the high pressure hose would strip the mirror coating off and probably damage the mirror surface. Well I really didn’t clean the mirror that way. I just said that in the title of the article to grab your attention. It’s similar to Shock and Awe Journalism.

So how did I clean the mirror? To start with, I just used every day common products. I did not use acetone or alcohol. Now there are web sites that will tell you it’s ok or they recommend acetone or alcohol. I’m not saying they are wrong, but it matters how dirty the mirror is. You can use different types of cleaners or a combination of cleaners, but that’s probably a personal decision. Because of the age of the mirror coating and this is a rough guess of 15 years, the type of coating it is, I decided to stick with a combination of soap and distilled water.

Another issue to consider is the Chip Factor. This is not a buzzword from the movie, The Matrix. When you are moving a mirror around to clean it, there are all kinds of reasons why you end up chipping the mirror surface or edge. Glass is strange at times. You can bang it into something and nothing happens and other times you fracture the edge or chip the surface. It happens!

Before Cleaning

Look at figure 1. You will notice the metal faucet is tied out of the way. The materials I used to clean are ( 2 ) one gallon bottles of distilled water and a box of 100% pure cotton, cotton balls. The synthetic material type can scratch or leave small abrasive streaks on your mirror. I also use a pair of disposable white plastic gloves. This keeps fingerprints off the mirror and you can grip the glass better, especially with large soapy mirrors. I washed the mirror in a plastic laundry tube. This helps to reduce the chip factor. In one of the distilled gallons of water, I added one teaspoon of Dawn liquid soap. This becomes a cleaning solution. The other gallon of distilled water is for rinsing off the mirror.

Cleaning the Mirror

Looking at figure 2. I poured the cleaning solution on the mirror and added about two dozen cotton balls. You swirl the cotton balls around in the solution. You do not scrub or rub the surface. Most of the dust, dirt and sticky insect residue from ladybugs and bees, will wash away. You may have to repeat this 2 or 3 times, but that’s ok. If you get a particle of something that will not dissolve, leave it alone. The reason behind this thinking is this, you will have to scratch it off and end up scratching the coating or leaving some kind of abrasion mark that sticks out like a sore thumb.

When you are done cleaning, raise the edge of the mirror up so the water will run off. Rinse off the soap and cotton balls with the other gallon of distilled water. Then rinse it again, until it looks clean. What do we do with the water drops on the mirror? You can take the corner of a paper towel and dab it (not rub or scrub) on the water spot and it should absorb the water. Because distilled water is used the water should evaporate and not leave any spotting. Hopefully! After I got done cleaning the 17.5 Coulter mirror I put it in the mirror box for safety and storage. So what is the next step with the mirror?

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Copyright © 2013, the University Lowbrow Astronomers. (The University Lowbrow Astronomers are an amateur astronomy club based in Ann Arbor, Michigan).
This page originally appeared in Reflections of the University Lowbrow Astronomers (the club newsletter).
This page revised Sunday, March 9, 2014 4:30 PM.
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