Cleaning a Mirror

Mirror Cleaning the Vermont Way

by Paul A. Valleli, from a procedure developed at ITEK Optical Lab about 1955

Recipe

1. Liquid Ivory Dishwashing Detergent, clear, no perfume, no coloring. ORVUS is a good alternative; it is Sodium Lauryl Sulphate - a well known dispersing agent
2. Clean Tap Water or better, Deionized Water, better still, a gallon or two of Distilled Water.
3. Cotton Swabs - Q-Tips, preferably with plastic handle
4. An absolutely clean Basin (sturdy Dish Pan if your mirror will fit in it)
5. Nitrile Gloves, wear a mask if you tend to spit while talking
6. Synthetic micro cloth Pads or Baby Wipes, Lint-free. It used to be natural cotton roll or balls but NASA has shown that they MAY contain a residue of cottonseed oil. That could be removed in a vapor degreaser but those are now pretty much banned because of Chlorine from things like Carbon Tetrachloride or Freon destroying the Ozone Layer.
7. Canned Air or Filtered Dry Nitrogen, 5 micron or better. Avoid compressed air, it usually has a residue of compressor oil and water vapor.
8. High Quality Lens Tissue, military grade - Berkshire Products, soft, NOT Crinkly like parchment.
9. Chemically Pure Acetone, or alternate Chemically Pure Alcohol. NO WATER added.
10. Nalgene Wash Bottles for Acetone and Alcohol.

Soaking the Dirt Away

To the basin add one gallon of luke-warm water (or more for large mirror) and ONE Teaspoon of Detergent. Stir. A 24-inch maybe should have 2 - 3 teaspoons. Add a clean sponge or pedestal and place mirror on top, face up. The detergent should cover the mirror. Let sit for several hours, even overnight. Rock the basin back and forth to swish the detergent across the mirror Let soak at least one hour. Many Stellafane Members swipe across the soapy surface with a bare hand. Absolutely no downward pressure. Not a good idea if you have been mirror grinding or machining parts that day - one metal splinter can cause an awful scratch.

Rinsing

Wearing Nitrile gloves, lift the mirror out and flood the mirror with Deionized or Distilled Water - Front & Back. If there is a water-break-free mirror surface (water-break free is when the water sheets across the mirror without leaving dry or oily spots) then flush the front side with Alcohol or Acetone, preferably from a  squeeze bottle. If the mirror is slightly warm, it helps to flash the solvent off. Blow dry any residue with canned air,

If you do not have a water-break free mirror surface, additional cleaning is needed. An additional, longer soak cycle could work. You could try to gently touch up a small spot with a  Q-Tip on stubborn specks. Or you could try Drag Wiping (see below)..

Air Dry

Tilt the mirror so that the acetone runs off. Pat the rear side and perimeter dry with cotton pads. Blow any droplets down to the lower edge with the canned air. Never shake the can - it may spritz water vapor, dust, and aerosols onto the mirror surface.

Drag Wiping Procedure

This is for use only if the above procedures do not fully clean the mirror and produce a water-break free surface. It brings additional risk of scratching the reflective surface, and needs to be done very gently.

If there are one or more trouble spots, like pollen grains, it may be necessary to "Drag-Wipe" that area with lens tissue. Fold each edge of about a 4-inch square of lens tissue until no ragged edges are exposed. Place one drop of Acetone on the pad and drag it across the problem area. It should instantly trap the contamination and flash dry. Repeat if there is still a residue. Only try water or Alcohol if Acetone doesn't work.

Storage & Shipping

Wrap the mirror in lens tissue and then paper towels, or newspaper, or cloth for shipment. Be sure the coated surface doesn't get rubbed or abraded during shipment such as truck vibration.