At 1:18 AM +0000 6/14/03, olympus-digest wrote:
>Date: Fri, 13 Jun 2003 17:59:38 -0400
>From: Chuck Norcutt <chucknorcutt@xxxxxxxxx>
>Subject: [OM] Well, I'm screwed..
>
>Albert said, in part:
>I cleaned it, but it seems whatever was in the soap I used, has pitted
>and dulled the plastic drastically.. (I have yet to use my OM in
>Thailand, last time I went, the 2nd picture, the entire metering system
>went out) So..
>- -------------------
>While I certainly wouldn't say it's impossible it strikes me as unlikely
>that ordinary hand soap has eaten your 1-4 screen. If it has I'm glad
>I'm not washing my hands with whatever you're using. What I can easily
>believe is that soap is still clinging to the teeny-tiny nooks and
>crannies of that very fine matte surface.
>
>Before giving up entirely I'd let that screen soak in warm water
>(preferably moving) for hours if necessary. Then, while holding it by
>its edges, give it a final high pressure blast from the faucet for a
>couple of minutes and stand it on edge on a paper towel to air dry.
>Then check it over again.
I agree with Chuck that it's unlikely that anything in handsoap could have
etched a OM screen. These screens are made of polystyrene plastic, which is
more resistant to chemicals than human skin, by a lot.
Some possibilities occur to me:
1. Hard water causing soapscum to deposit on the screen. The classic solution
is to soak the thing in vinegar, which converts the scum back to oil, removal
of which is discussed next. If vinegar isn't strong enough, use hydrochloric
acid (aka, muriatic acid) or even sulpheric acid (battery acid). None of these
acids in the strengths normally used will harm polystyrene unless you soak the
screen for days. Not that you have anything to lose.
Muriatic acid is used to clean masonry, and can be bought in hardware stores.
Battery acid is used for lead-acid batteries used in cars, motorcycles, etc,
and can be bought in auto-parts stores.
2. Many soaps have oils or greases such as Olive Oil or Lanolin in them, to
reduce the drying effect on the skin. Polystyrene attracts oil very strongly,
and would form a hard-to-remove film. Unfortunately, such films are not very
good optically, unless very thin.
If the oil is left in place too long, it may begin to diffuse into the plastic,
making complete removal impossible.
The best way to remove them is very hot water, dishwashing detergent, a small
soft brush with very fine bristles, and rubber gloves. Basically, this is the
high-tech version of washing the dishes. Use a plastic tub that holds at least
a liter of water, and is wide enough that both hands will fit at once. Put
some detergent in the tub, and fill halfway with hot water straight from the
tap. With gloved hands, wash the screen with the soft brush while holding it
underwater. Scrub in the direction of the grooves in the plastic. Rinse with
hot water straight from the tap. If necessary, wash again, rinse again. Dry
by patting with a freshly cleaned cotton towel. Do not soak the screen in the
hot water; it may warp.
One can test this method out on one of those clear plastic boxes sold to store
small parts before trying it with a screen. This will allow one to determine
if the water is too hot, but I don't think that domestic hot water is ever too
hot for polystyrene, but an experiment will settle the issue.
If one is washing the screen just to remove dust and the like, and perhaps a
fingerprint, use the dishwasing trick, only with very warm water, but not
scalding hot. But I never clean screens, I just blow them off. The less
handled the better.
Joe Gwinn
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