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Top Plate M6 strange marks

Discussion in 'Leica Camera Chat' started by PeteE, Jun 29, 2017.

  1. PeteE

    PeteE Well-Known Member

    I have some strange black marks on the top plate of my 1986 M6 which do not clean off -- I an see dust around the hot shoe which needs a clean with a cotton bud ( 'Q Tip' for you Yanks ) but these look as if the metal is going rotten !
    Top Plate Marks.JPG
  2. Roger Hicks

    Roger Hicks Well-Known Member

    Dear Pete,

    Certainly weird. Looks like corrosion, where something has been in contact with the metal for a long time. I've never seen anything quite like it. Have you tried Solvol Autosol?


  3. Fishboy

    Fishboy Well-Known Member

    Isn't the M6 the model where they used a zinc top plate under the chrome finish?

    I was under the impression that it only takes a microscopic hole in the chrome coating that goes through to the zinc to allow the corrosion to spread, although I thought that resulting corrosion looked like bubbles on the surface rather than what you're showing in the picture.

    Cheers, Jeff
  4. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    Certainly corrosion. However it is not likely to cause functional problems, and it can always be covered with black gaffer tape.
  5. Craig20264

    Craig20264 Well-Known Member

    What material is the Top Plate Pete?
  6. PeteE

    PeteE Well-Known Member

    I keep M6 body wrapped in a Canon Lens Blue Cloth pouch- not in contact with any other metal . I had a go to remove marks with Cotton bud wet with a little dilute washing up liquid and they seemed to go. I do not know what metal the top plate is but it 'may' be Zinc.
  7. 0lybacker

    0lybacker In the Stop Bath

    Hi Pete, think Roger H and Jeff are right. Have you spoken to Leica? They have changed materials over the years and I think did not originally do the M6 in chrome. Yours could be an early one.

    Chromium will degrade in time if attacked by the right (wrong) substances. My 'first proper camera', a s/h Agfa Silette in mid-sixties, is 'decaying' in places, in one or two spots the chromium is actually 'bubbling up' from underneath. Have same happening on a bequeathed Zeiss Nettar. No consolation for you, I'm afraid. Have you owned it from new? Cheers, Oly
  8. Fishboy

    Fishboy Well-Known Member

    I think you've got the wrong end of the stick here!

    Leica top plates were usually made of brass and either chrome-plated or lacquered in black. For some of the M6 models they made the underlying top plate of zinc instead of brass, but still with the two standard finishes of chromium plate or black lacquer.

    The issue was to do with how chromium on zinc reacts compared to chromium on brass. The brass version was pretty inert and a scratch in the chromium plate didn't have much of an effect, however the zinc was more reactive and a scratch in a chromium-plated zinc top plate tended to result in bubbling.

    Everything you say about the way a chromium finish can decay is absolutely right, but the point I was making was that on the M6s, the underlying material of the top plate is a factor as well.

    Cheers, Jeff
  9. El_Sid

    El_Sid Well-Known Member

    The old chrome bumpers on cars used do this...:(
  10. Roger Hicks

    Roger Hicks Well-Known Member

    Dear Nigel,

    True. Why didn't I remember that?


  11. GeoffR

    GeoffR Well-Known Member

    Chromium plating is porous and offers no protection for the underlying metal. High quality Chrome plating is a four stage process, Copper on the base metal, then Nickel and finally Chromium. The Copper is, I recall, for adhesion, the Nickel provides corrosion protection and the Chromium looks nice. Brass is pretty corrosion resistant so Chrome plate on brass will be fine as it is purely cosmetic. Zinc is also corrosion resistant, think galvanised steel, but isn't as good a base for Chrome as is brass.

    I suggest that you contact Leica and see what they can offer, probably a replacement top plate if they are available.

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