Archived posting to the Leica Users Group, 1999/08/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Yes, David, all the M4-P's with flush windows have zinc top plates. The reason why the cameras with brass top plates in black chrome get "silvery" on the edges instead of braising is because of the nature of the black chrome plating process. It is not a single black chrome plate, but rather a series of platings applied to the metal part. On the zinc top plates, first a flash coat of copper is applied, then nickel plating, chrome plating and then the finish black chrome plating. I believe the copper flash coat was not used on the brass top plates. Since the bright chrome plating is very durable, it is rare to wear past this on the black chrome cameras. Black paint cameras on the other hand do not have these coatings and wear through to the brass rather easily. Zinc does have some interesting properties. It resists dents like nobody's business, but will crack under extreme stress. It is also somewhat porous, which makes the copper flash coat necessary. If the zinc is scratched down to the bare metal, it will begin to oxidize and tun into a powder around the scratch. Zinc is not as ductile as brass. That's the reason the zinc top plates lack the fine detail of the brass versions, hence the flush windows. Zinc is also cheaper to make, as they are cast and not formed under high pressure in a gigantic press like the brass top plates were. BTW, I've heard that Leica will be going back to brass top plates on the M cameras in the near future. Bill Rosauer