Ron Guth: Under the Edict of October 1738, all of the earlier French coins of 30 Deniers were recalled and replaced with a new billon coin with a value of 24 Deniers. These "Double Sols" or "Sous Marqués" were issued from 1738 to 1864. In the earliest years, all of the French mints produced Double Sols; in later years, only the Paris and Strasbourg facilities were used.
Although billon is already an alloy with a low percentage of silver, many of the later issues were debased even further. In extreme cases, the only silver in the coins was a thin plating applied over the surfaces. Thus, it is not uncommon to find circulated examples with a copper color. Conversely, examples with a high percentage of the original silvering still remaining are sometimes quite rare or non-existent.