The article to be plated is the cathode in an electrolytic bath with an anode as the other terminal.

Chromium Plating

Chromium plating is an electrochemical process in which a uniform layer of chromium is deposited on a cathode. In most plating operations, the anode is made of the material which is to be plated. But chromium plating is the exception because the anode is an inert lead alloy which merely supplies electrons to the solutions. These electrons react with the chromium in the solution to deposit on the cathode.

Pure chromium anodes are too expensive and impractical to use.
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.
Therefore, a lead or lead/antimony alloy is used and because of its inert properties, these anodes do not need to be replaced as often as other plating anodes.

from web
Umut