These are stamped marks found on many, but not all daguerreotypes. These stamps are
usually located along the exterior edges of the plate, making them invisible when the
daguerreotype is sealed with a brass or paper mat. Plate marks usually consist of initials,
symbols and sometimes numbers. The number most commonly found is 40, indicating 1
part silver to 39 parts copper, the physical makeup of the plate. These plate marks can
also aid in dating the images.
An interesting plate mark was found on a daguerreotype entitled The Carpenter in
Canada, taken circa 1850 by an unknown photographer. The plate mark is located in the
bottom left corner and includes a six-petal flower as well as the word "DOUBLÉ". Below
this is a stamp of a lamb with a cross, known as a "Paschal Lamb". Below this is the
name "A.GAUDIN" and the number 40.
Research indicates that the manufacturing company was Alexis Gaudin & Bro., from
France. It is unknown when manufacturing began, but the plates were in production until
at least 1856. This plate was widely used in North America around 1850 to 1855, with the
peak year being 1853. This corresponds to the portrait's estimated date of 1850. The
word "DOUBLÉ" in this case means that it is plated silver, rather than dipped, a
manufacturing process of daguerreotypes. Once again, the number 40 denotes the
portion of silver to copper found in the plate.