Revised 11/1/99

D. Hilyard

Lick Obs.

Cleaning of some of the optical surfaces in the ESI Spectrograph and Spectrograph Camera will be necessary occasionally. Since all the surfaces are either uncoated or coated with a hard coating or overcoat, the procedure for cleaning all the surfaces can be performed using this procedure.

The first cleaning step should be a blow-off of the surface using dry nitrogen or other dry air supply, blowing at a grazing angle to the surface. The air supply should be about the same temperature as the optics being cleaned. This step is necessary to remove particles or debris that are large and coarser in nature that could cause scratches if wiped across the surface in later cleaning steps. A Microduster canned inert dusting gas can be used with caution. They often leave a residue if the can is not held upright.

Following the blow-off, a few liquid washes can be used, depending on the amount of contaminates or stains left on the surface. If there is still substantial debris that cannot be loosened with blowing off, the best wash is a mixture of Orvus W.A. Paste (sodium lauryl sulfate) and acetone. The Orvus acts like a soap and the acetone a solvent that dissolves some contaminates and cuts the soap film. Mix about 1 tablespoon of Orvus paste in a 500 ml squirt bottle of water, then add 10 to 20 ml of acetone to the mixture, and shake well. This solution should also be within a few degrees F of the optical surface being cleaned. The wipe material depends on the nature of the debris on the surface, the optic material, and the area to be cleaned. A soft material lens will require a cotton ball or cotton gauze pad wipe, well saturated with the Orvus/acetone solution, and using a delicate swabbing or patting motion to pick up the debris onto the cotton swab without wiping it across the surface. Repeated swabbing may be required to pick up the debris that may scratch if wiped across the surface. If the optic is large, and the material quite hard, the best wipe material is a Kimwipe or Kaydry. Well saturate the Kaydry with the Orvus/acetone solution and use a delicate swabbing or patting motion to pick up the debris. Use clean areas of the Kaydry for each new surface area, and switch to a new Kaydry when contaminates fill the used one.

If after the blow-off, the surface looks free of scratch producing debris, a wash of methanol or isopropanol can be used on either a cotton pad swab or a Kaydry. Still use a delicate swabbing or patting action to lift the contaminates from the surface rather than wiping them across the surface.

After the Orvus/acetone wash or the methanol wash the surface can then be wiped with either a tissue or lens tissue moistened with methanol or isopropanol. A method that works well for the wipe is to fold the tissue or lens tissue into a triangular shape, moisten the tip and use the index finger behind the tip of the wipe to point the wipe across the surface in overlapping side to side strokes. If the wipe is too wet, a noticeable wet film will be left in its path. If too dry, the wipe won’t glide easily, and may abrade the surface. A final wipe with a good grade acetone (A-18 or A-19) using the same wipe technique with tissue to lens tissue will remove the methanol film. It may take several wipes to cross the surface if it is large of or if the wipe becomes dirty. The overlapping wipe technique is used to avoid trailing wipe marks. This technique takes practice to achieve a cleanly wiped surface without wipe or solvent residue trails.

Orvus W.A. paste is a Proctor and Gamble product and can be found in the equestrian section of a feed store. An alternative is Ivory Liquid Soap, the white creamy hand-soap, and not the dish detergent. A good lens tissue for wiping optical surfaces is made by Alden Corporation. An alternative is Kleenex tissue free of scents or oils.

David Hilyard

UCO/Lick Observatory