Archived posting to the Leica Users Group, 2002/03/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]The black chrome on the Leica M's (and R's too) is a process similar to the regular bright chrome. The process involves the use of a chromium salt (I have only seen it as Eloxal and with a Leitz Germany label on it) and some rather nasty chemicals such as cyanide and acid. The process involves coating the piece to be plated with acid copper (when done on Zinc or other alloys) and then a layer of nickel plating and lastly the black chrome. The wear on a black chrome camera usually involves wearing the black chrome off and having the nickel show up as a silvery finish and if you persist you can wear it down to brass underneath. This takes a lot of film though! I have a M4P that I bought new in 1981 that has worn through to brass on the back and top, but most of the wear is down to the nickel plating. The alloy top-plate (a zinc die-casting) needs the acid copper to seal the pores in the casting as it otherwise can react with salt-laden air and start a galvanic reaction. There was a small series of R6's that suffered from this and the black chrome plating could blister and the plating peel off. I have seen diecast alloy baseplates at Leica Midland in the early 1980's but they were never put into production as the structural strength of the "hinge" part of the baseplate was questionable. Zinc alloy is very strong, but upon impact it can crack rather than dent as brass would do. All M baseplates are made from brass and some of the "special finishes" on the M6/M6TTL had brass top-plates and, to my knowledge, all of the M7's will have brass top-plates. Using brass allows Leica to adapt production to a variety of changes, such as the Millenium camera (and the Japanese Hansa/ICI/Dragon etc) with the M3 rewind as well as allowing engravings on the top-plate rather than having expensive casting molds done for each variation. The LHSA black paint cameras also have the brass top-plate as alloy is notorious for providing a bad surface for painting. Anodizing is a different process as it requires an aluminium alloy base and the colouring is "sunk" into the surface of the material. Plating builds up on the top of the surface and will change dimensions of the piece plated. I seem to remember that the first black chrome M's were the M4 Midland and a small series of M4 Wetzlar with the M5 being the first production model in black chrome. The zinc diecast models started with the M6 and the late "flush windowed" M4P's. My personal preference is brass with black paint as it tends to look pleasantly used with the brass showing through. All the best, Tom A Tom Abrahamsson Vancouver, BC Canada - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html