Notes:
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.  Additionally, a new Sol valued at 12 Deniers was struck from 1738-1748.  The following mints produced this coinage: Paris, Rouen, Caen, Lyon, Poitiers, Limoges, Bayonne, Toulouse, Montpellier, Riom, Dijon, Perpignan, Reims, Nantes, Troyes, Lille, Amiens, Bourges, Rennes, Aix, Metz, Strasbourg, and Besançon.

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.

Images courtesy of Ira & Larry Goldberg Coins & Collectibles, Inc.

Significant examples:
1740-A PCGS MS-62 (illustrated above).  Ex - Paul Arthur Norris - Ira & Larry Goldberg Coins & Collectibles, Inc.'s "Pre-Long Beach Sale", September 23 & 24, 2002, Lot 43, illustrated, where it was described as follows: "PCGS graded MS-62. A rare issue in any grade, this particular example is the only one graded by PCGS according to their online Population Report, giving an indication how few of this date are found. The surfaces are slightly rough probably as made, and the coin has light silvery gray color with hints of dark colors intermixed. Fully struck by the dies, and with no other problems worthy of note.
These were issued for the French colonies in Canada, and many circulated into the Louisiana Territory as trade was flourishing at the time. Breen notes these to be "rare", and given that this is the only example of this date graded by PCGS, they may be quite rare."

Sources and/or recommended reading:
"An Illustrated Catalogue Of The French Billon Coinage In The Americas" by Robert A. Vlack