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[at-l] Re: fog on glasses

"Benjamin Brent Forbis" <bbforbis@eos.ncsu.edu> writes:
Subject: [at-l] hiking by braile method

>In responce to hiking in fog (ie.by braile) as long as there  is 
>any substance that can put a thin film between the glass and exposure will 
>prevent the fogging. As a scuba diver I have heard of a raw potato, a very 
>weak solution of baby sampoo/h2O, spit(the cheapest and most portable)

I've read that Russians rub potatoes on their windshields to produce a 
water-repellant effect, because windshield-wiper blades are hard to get and 
are often stolen.

Rain-X (tm) is absolutely wonderful on windshields.  It's a wax-like 
substance that prevents wetting; the rain forms little balls and blows
away.  The faster you go, the better it works, and it's pretty, like being
inside a bottle of Sprite!  Car wax on glass works similarly but not nearly
as well.  I haven't tried Rain-X on eyeglasses; it should work well in
rain, allowing you to shake the water off the lenses.

Rain-X is NOT effective against fog.  For fog you need the opposite effect,
i.e., a surfactant (wetting agent) which destroys surface-tension and makes
water spread in a uniform layer.  Soap does that, which is why baby shampoo
works, but it must be kept wet and reapplied frequently to be effective,
and may form a cloudy film when dry.  I've never found a de-fog compound
that's truly satisfactory.  Stuff from an auto-parts store had no
noticeable effect on the inside of a windshield or on a bathroom mirror.

 --  Frank     reid@indiana.edu
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