Both the top cover (including the separate rangefinder housings of models II to IIIb, and the housing under the shutter dial of all Leica I and Standards) and the baseplates were of drawn brass. Black finishes were a shiny black etching ground lacquer, probably applied directly without any ground. How Leitz prepared the brass for the chromium plating I don't know; general practice in the surface treatment business seems to be a thin preparatory layer of copper.
Early chroming from about 1933 or so seems to be shinier than later practice. The quality of the chrome deteriorated during the last years of World War II and the early peace years, as Germany had a bad shortage of chromium, which is of course a strategic material. This was the reason behind the dark-grey cameras from the war years.