Joel Wilcox wrote...
I herewith quote Dr. John from about one year ago on this topic and a
more agressive cleaning method:
"Lens tissue wrapped around a narrow flat object, dipped in denatured
alcohol
works for me. Don't press too hard on the mirror as the silver can come
right
off if you trap a piece of grit in there. If there is old mirror foam
in the
corners, that'll smear around alot and you'll have to clean it 10 to 20
times
to get it all off.
John
Camtech"
My recollection is that several list members were appalled at this
method
of cleaning the mirror. I've had several cameras through John's shop and
the mirrors all have come back looking good.
----------------------------------------------------------------------
The proof is in the pudding. The mirrors have all come back looking
good. John speaks loosely of "silver" on the mirror. Since long before
the OM-1 was made first surface mirrors have typically been coated with
aluminum and not with silver. Silver is an excellent coating for mirrors
(for the first 5 minutes) because it has a higher reflectivity. But...
it's soft and quickly tarnishes. When used on a mirror it must be
overcoated.
Aluminum, also "tarnishes" but the coating that forms when exposed to
the air is aluminum oxide. The aluminum oxide layer is clear and
extremely hard... which is why aluminum oxide is also used as a grinding
compound. It's harder than glass.
Of course, both the aluminum coating and the oxide layer are extremely
thin and some little piece of grit can cause a scratch. I wouldn't
suggest using a liquid unless it was really needed but, as long as
you're not dragging grit around the surface, cleaning with a liquid like
lens cleaner should cause no harm.
Chuck Norcutt
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