The camera that started the trend of black finish was not the Leica MP, but the Nikon S2. The black paint Nikon S2 was introduced in October 1955. The black S2 is plated with black nickel and then painted.
The Nikon rangefinders possessed a fit and finish the equal of the Leica, although some folks mistake the inherent play in the fit of the detachable back for a lack of bodily solidity. It is not. In terms of finish, the Nikons sometimes bested the Leica. Unlike Leitz, the white markings are engraved – on the M3, M2 and M4 only the serial number is engraved – on the Nikon S2, all the white numerals, lettering and indications are engraved by hand.
The first of black M Leicas was a run of 5 black paint M3’s followed shortly by the famous black MP’s. Leitz made 150 of the black MPs. The paint on these cameras is very dull and thin.
In 1958 Leitz introduced the M2 that was also made in black, the same finish and paint type that was used on the MP: dull and thin. Leitz produced 500 of the M2’s in this run of black paint production.
Towards the early seventies Leitz offered a service for those who were not happy with the flaking and bubbling paint on their early black M2’s. All the black parts were replaced by new ones and the original number was engraved, but slightly higher than the old ones from the fifties. The type of paint was the same of that of the black paint M4 and Leicaflex SL.
For some reason lost to time, Leitz did not have a restoration service for the M3 as they did for the M2. However, owners could have their chrome M3’s transformed to black paint. These transformed cameras are very rare, due to the high cost. They were often made to match the Noctilux 50mm f/1.2, a black finished lens.
The style of the engraved number will date the camera a bit. This one does not have any spaces in it’s number, so it can date from the M5 era when the numbers were engraved into the accessory-shoe without spaces. Note the position of the engraved serial number, just a bit lower than the M3 engraving.
*Thanks to Eric van Straten for the photos and expertise. This is essentially a verbatim reprint of a fascinating tutorial posted by Mr. van Straten elsewhere. Mr. van Straten is an amazing source of information for all things Leica film rangefinder related.