Interesting and at this juncture, I'd say that the preponderance of evidence points to Canon Fanget or Fanget & Co. owning the cupped-up duck trademark stamp. Maybe additional info will shore up this hypothesis or point to the actual fella.

The following blog/thread on St. Etienne tube making just might be informative and an English translation most insightful?

http://gravure.blog.fr/2011/03/28/la-fabrication-des-canons-a-saint-etienne-suite-10904999/

Kind Regards,

Raimey
rse