Oxidation/corrosion spots in mirror box

Pentode · Dec 25, 2017

Hello all, and happy holidays!

I've just gotten around to a Minolta XD-11 body which I found late last summer at a flea market.

The lens box has whitish spots all over the side walls, which I believe to be oxidation. The spots are only on the side walls. There are none on the top or bottom or back walls of the mirror box and there are no signs of it anywhere on any other part of the camera. The body is, in every other way, pristine.

My first thought was that it might be fungus (there are signs of fungus beginning on the rear lens element, which I doused heavily in peroxide several times) so I hit it with peroxide a couple of times, but I'm inclined to think it's oxidation. I plan to hit it with peroxide and ammonia just to be sure.

Given this situation, would you:
A) Ignore it?
B) Apply some flat black paint to it?
C) Other?

Thanks for any and all thoughts!

Pentode · Dec 25, 2017

Sorry.... pics or it never happened, right?

shutterfinger · Dec 25, 2017

Go to Target, Walmart, CVS, Wallgreens and get a pint of 91% Isopropol Alcohol and some cotton swabs. Wash the spotted areas with the alcohol and cotton swabs.
The white spots resemble magnesium corrosion.

Pentode · Dec 25, 2017

Thanks, Shutterfinger! I have some in the house already. I'll give it a try.

shutterfinger · Dec 25, 2017

If it washes off with the alcohol then its mold, if not its corrosion. For corrosion buff off with a scotch brite or similar then paint with flat black paint.

zanxion72 · Dec 26, 2017

Or, lock the mirror up and carefully paint it with matte black enamel paint. It will cover it perfectly and stop the oxidation too.

lantau · Dec 26, 2017

Mine looks similar. Looking at it 'my spots' look weaker and the surrounding areas have a white sheen when window light is reflected on the wall by the mirror. I never really paid it any attention. The effect seems to be minimal, if any.

PS: Isn't that called Schneideritis?

paul ron · Dec 26, 2017

aluminum acne. get the mirror to stay up. using your vacum cleaner near the mouth of the lens mount, carefully sand those raised bumps off. then with a brush, paint it with rustolium ultra flat black.

schneideritis is a lens edge blackening problem. yes it looks similar when looking down into the lens, white pimples.

Pentode · Dec 26, 2017

I have flat black enamel railroad model paint in the house (for just this sort of thing) so it won’t be any problem to cover them over. I don’t think any sanding will be required as the spots are not raised significantly.

It’s interesting that my other, older XD-11 doesn’t have this issue. I have no way of knowing how they were treated before they belonged to me, though, so I guess it’s not that odd. My older one’s been with me over 20 years. This new one with the spots might have spent those years in a wet basement.

Thanks for the tips!

paul ron · Dec 26, 2017

as long as those pimples arent hindering mirror travel, you can paint over it. id gently sand em down as a perventative measure... but thats my ocd.

Pentode · Dec 27, 2017

paul ron said:
as long as those pimples arent hindering mirror travel, you can paint over it. id gently sand em down as a perventative measure... but thats my ocd.

They’re very flat - far from interfering with the mirror in any way. Even with a vacuum I’m hesitant to make dust inside an otherwise very clean camera. I’ll just hit them with alcohol to get them good and clean and then use the flat black model paint. Should work fine.

Now my only problem is finding the time! Double shifts for the next two weeks....

shutterfinger · Dec 27, 2017

Pentode said:
I’ll just hit them with alcohol to get them good and clean and then use the flat black model paint. Should work fine.

but the corrosion will continue, a bit inhibited, and flake the paint off.
Canned air with the shutter on B and back open will remove the sand dust.

mike c · Dec 27, 2017

I have the same spots on the inside back of my 150mm Hassey lens, been there ever since I toke the lens for a walk on the Huntington Bch Pier, fifteen years ago, the corrosion never spread.

shutterfinger · Dec 27, 2017

mike c said:
I have the same spots on the inside back of my 150mm Hassey lens, been there ever since I toke the lens for a walk on the Huntington Bch Pier, fifteen years ago, the corrosion never spread.

The rate of the increase in the corrosion depends on the environment the camera/lens is stored and used in.

E. von Hoegh · Dec 28, 2017

I'm sitting here, shaking my head, absolutely flabbergasted that anyone would reccommend SANDING the inside of the mirror box of an assembled camera. Just unbelievable.

jim10219 · Dec 28, 2017

Definitely don't use peroxide! Peroxide causes many metals to oxidize. It's just about the worst thing you can do.

I wouldn't sand it. Maybe run something along it to free up any loose pieces (like an old tooth brush or your finger). Do it with the camera upside down so the dust falls out, away from the mirror box. You don't have to get crazy with it. Leaving some oxidation behind is okay, and probably a better option than ruining something by over-cleaning it. You just want to get rid of any loose stuff that may fall out and cause issues later on. Then, paint it with a matte black paint oil based paint. That should seal it off from the air and help to prevent further oxidation.

Pentode · Dec 28, 2017

That’s the direction I’m headed in. I simply plan to encapsulate the corrosion with flat black enamel paint. I don’t expect further troubles with that approach.

Thanks, everyone, for their ideas and perspective!

E. von Hoegh · Dec 28, 2017

jim10219 said:
Definitely don't use peroxide! Peroxide causes many metals to oxidize. It's just about the worst thing you can do.

I wouldn't sand it. Maybe run something along it to free up any loose pieces (like an old tooth brush or your finger). Do it with the camera upside down so the dust falls out, away from the mirror box. You don't have to get crazy with it. Leaving some oxidation behind is okay, and probably a better option than ruining something by over-cleaning it. You just want to get rid of any loose stuff that may fall out and cause issues later on. Then, paint it with a matte black paint oil based paint. That should seal it off from the air and help to prevent further oxidation.

Hydrogen peroxide = H2O2. Twice as much oxygen as water. Pure hydrogen peroxide is used as an oxidiser in liquid fuel rockets.
Matte or flat black oil based paint, I use RustOleum flat black, both spray and with a brush. Paint over the spots and keep the camera in a dry environment, likely you'll have no more trouble.
Don't spray the mirror box, and if you feel the need to scrape at the spots (I wouldn't) vacuum the box, do not use compressed or canned air which will blast the dust and grit into every nook and cranny.

Pentode · Dec 28, 2017

Thanks. I feel no such need. The spots will remain unscraped and will be covered with flat black paint.

New York City gets very humid in the summer but not so much that I’ve had any problems with rust, corrosion or fungus in the past. I use basic common sense when I store my gear and I don’t expect this will be an ongoing problem.

This camera body is so clean otherwise I can only assume that it was stored in a very damp environment, unused, for many years prior to my owning it.

Between paint inhibiting further corrosion and better stewardship my problem should be solved.

AgX · Dec 28, 2017

There is still speciall dull black enamel available.
Tetenal still offer it, though meanwhile only as spray. Alternatively one could use blackboard paint, which looks similar.

paul ron · Dec 28, 2017

E. von Hoegh said:
I'm sitting here, shaking my head, absolutely flabbergasted that anyone would reccommend SANDING the inside of the mirror box of an assembled camera. Just unbelievable.

oh, dont use the belt sander, use an orbital with 80 grit! that is the only way to get it all.

shutterfinger · Dec 28, 2017

E. von Hoegh said:
do not use compressed or canned air which will blast the dust and grit into every nook and cranny.

Only because you don't know how to use canned air properly.

E. von Hoegh · Dec 29, 2017

shutterfinger said:
Only because you don't know how to use canned air properly.

https://en.wikipedia.org/wiki/Dunning–Kruger_effect

paul ron · Dec 29, 2017

E. von Hoegh said:
https://en.wikipedia.org/wiki/Dunning–Kruger_effect

because you dont have the skills or understanding to do what has been recomended, doesnt mean these methods are wrong... perhaps in your mind, but not in the hands of a skilled individual.

how long have you been in the business repairing cameras?

if you cant dance, become a critic?
shake your head!

shutterfinger · Dec 29, 2017

I can take any piece of equipment regardless of how fragile that anyone has vacuumed and declares free of debris and blow out some more debris with compressed or canned air.

Oxidation/corrosion spots in mirror box

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