FWIW, I've found that simple hosing followed by drip dry restores about 3/4 to 90 % or so of clean (as opposed to clean and new) performance. With a weak solution of dish soap (not dishwasher soap) and a gentle scrub with a soft cloth followed by a simple hose rinse and drip dry, I seem to be able to restore about as much of possible performance loss from dirt as is likely to be achieved. I try not to touch the glazing and use (clean) cheap cloth gloves, but some inadvertent skin on glass almost always occurs. Windex works great on smudges and guano and seems to leave no residue, even when viewed through polaroid lenses for what that that observation may be worth.
I haven't been able to find a quantitative measure as to whether or not the soap harms performance, but at this time I doubt that it harms anything when used with common sense. All the informed stuff I see on that subject, suggests some form of soap as part of the cleaning regimen. A Sunpower white paper suggests no ARC deterioration from Windex or other such cleaning products. I suspect the nature of the fouling may have something to do with how particular cleaning products interact with ARC coatings, but if a surface treatment can't stand up to mild dish soap without deterioration, I'd doubt its long term suitability.
I haven't been able to find a quantitative measure as to whether or not the soap harms performance, but at this time I doubt that it harms anything when used with common sense. All the informed stuff I see on that subject, suggests some form of soap as part of the cleaning regimen. A Sunpower white paper suggests no ARC deterioration from Windex or other such cleaning products. I suspect the nature of the fouling may have something to do with how particular cleaning products interact with ARC coatings, but if a surface treatment can't stand up to mild dish soap without deterioration, I'd doubt its long term suitability.
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