The overview of French hallmarking on this website (https://www.925-1000.com/Ffrench_marks.html) indicates that all French maker marks within a square/rectangle cartouche are silverplate. I started wondering if the inverse were also true, in that all French maker marks within a diamond/lozenge cartouche must always indicate solid silver.
After reviewing the Christofle marks (also on this website https://www.925-1000.com/a_christofle.html), one image depicts a silverplated spoon with a diamond/lozenge maker mark, so it appears the diamond/lozenge cannot always be relied upon to indicate solid silver by itself.
Next, I came across a website (http://www.ascasonline.org/ARTICOLOMARZ180.html) that states that from 1862 onward, the Christofle mark was placed within a rectangle and alludes to "new laws being imposed by the French government" as the reason for the change but doesn't go into great detail about this.
Putting this together, it seems the following statements can be made (neglecting the case of forgeries):
- French maker marks within a diamond/lozenge cartouche DURING/AFTER 1862 should always indicate solid silver
- French maker marks within a diamond/lozenge cartouche PRIOR to 1862 may be solid silver OR silverplate
- French maker marks within a square/rectangle cartouche from any period will always indicate silverplate
I would appreciate someone letting me know if these statements are valid. Thank you,
As a side note: (http://www.ascasonline.org/ARTICOLOMARZ180.html) states that for Christofle specifically, the thickness of the plating is a small number located between the balance scales on the Christofle maker mark and the number 55 pictured above would actually designate the year of manufacture (1855).