Bill is completely right:
The technical translation of JL Princelle can lead an error:
Really, in the 1930s in 1950 it was current, for mechanicians who could not Nickeler the mechanical surfaces in finish, "to scratch" surface to polish them by small touches. They used to make it a "Scraper" (in French) which was a manual tool to rectify with a maximum of precision surfaces for "good finish" looking.
I even personnaly ,used this tool during my technical learning to the college in the years 55 - 60: it was a boring and slow work.
For example, people of the factory Bugatti made the same matter on the aluminum dashboards of automobiles, but by making turn the tool. It gave this aspect if private individual of finish.
For our Fed, these small scratched surfaces erased the irregularities of the galvanoplastique cover of the manufacturing by approaching the luxury criteria of some item in silversmith's trade of this time, by mitigating the lack of raw materials.
Actually when we look well at an object galvanized with some zinc as ancient pans or basins) we can believe and be allowed abuse by the aspect.
To my opinion, it adds a little more to the interest that we carry in these cameras because it shows well that they are objects made by true mechanics workers.
To be contested

???
Alain
(PS : to day , I am very tired but happy , because the phénomenal Bièvres friend's meeting )Thanks to all...