In order to prevent and detect fraud of hallmarked silver articles, French authorities instituted by Ordinance of 1st July 1818, a system of countermarks on the opposite side of the guarantee mark. These countermarks are known as bigornes.
The term bigorne litterally means two-horned anvil or two-beaked anvil and refers to the shape of the projecting ends of the anvil. Each anvil has two striking areas, one flat and one of rounded shape. The rounded horn served to mark hollowware and the flat horn was used to mark flatware.
The projecting ends of the small anvil were intricately engraved with varied and finely drawn representations of insects. The silver article was placed on the beak/horn of the steel anvil and when the guarantee mark was struck, the force of the strike created a counter-impression of insects on the underside of the article against the anvil.Bigornes introduced by Ordinance of 1st July 1818 and used from August 1819 till May 1838
There are three sizes of bigorne marks, having randomly arranged insects on a plain background, except for the small bigorne which had both a rounded and a flat end :
-The large bigorne with a horn on which the six different insects are engraved inside various frames (triangle, pentagon, indented parallelogram, lozenge, etc).
-The medium-sized bigorne with a horn bearing engraved insects, but not so many as on the large bigorne. Both bigornes are the same for Paris as for the Provinces.
-The small bigorne with two horns, one flat and the other rounded, bearing engraved triangles and lozenges with linear designs and letters.Bigornes instituted by a Decree of 30th June 1835, put into use on 9th May 1838 (modified in December 1846)
This system is even more sophisticated than the preceding one, because the insects are engraved aligned in relief and separated by parallel zigzag molded borders. This series was further distinguished by having one set for Paris and another set for the Provinces.
The surface of the anvil is covered with varied and finely drawn engravings of various insects which mark the underside of the silver article when it is struck on the upper side with the guarantee mark. The assayer placed the item on the horn of the anvil, then placed the Minerva (or other) punch on the item, and stroked the Minerva punch with a mallet. Through the force of the strike both marks were created simultaneously. For this reason a bigorne mark will be found opposite the guarantee mark. The bigorne dies are so complex that two similar strikes could not be obtained.
There are three types of bigorne used according the object size : large (16 bands), medium (13 bands) and small (21 bands). The rounded horn and the flat horn are used depending on the shape of the article to be marked.
For Paris the insects are in profile and for the Provinces (Départements) the insects are in bird’s eye view.
The borders separating the bands of insects are hollow except on the medium sized bigorne and on the rounded horn of the small bigorne. In these cases the tiny grooves are covered with dots; these serve as a support in the marking of very thin articles and also prevent the marks to appear only on the surfaces resting on the insects.
Ref : www.silvercollection.it/dictionarybigorne.html