Smollett said:
I have read that there were more French flints used in America than English ones (they've even been excavated in British campsites).
Smollett
Historically, French Flints were MUCH more popular in Colonial America than English Flints. They were often imported by the French around the Louisiana Territory or smuggled in by Dutch and other traders to other English Colonies, BUT it was because of the
shape of the French flints and not so much the material it was made from. French Flints were shaped like what we are used to seeing on English Flints today.
It seems the French were smart enough to carefully guard the secret of how to make their better shaped flints for a long time.
English Flintknappers were making "Gunspall" or Wedge Shaped flints right up to the middle 1770's. (Most of us looking through a pile of flints today would chuck this type to the side and ignore them.) Gunspall Shape Flints did not give as good of sparks and did not last as long.
There is a good deal of information on these Gunspall flints in
Colonial Frontier Guns, by Hamilton. Hamilton mentions the English did not know how to make flints in the "French Style" until some French Flintkappers were captured and brought to England during the AWI. Bailey has some quotes how "New Style" Flints were begun to be offered to and ordered by British Ordnance around 1777 (I think without checking) and they took the place by storm. These were shaped by what was then the "French Style" and not the old English Gunspall style.
As far as in modern times with French Amber flints, I have never found ones in the sizes that were correct for my guns. Most of the " Original Musket Style, French Amber Flints" that were sold in places I was familiar with, were WAY too large for modern Repro Muskets. (I think they were actually made for Cannon Locks and/or Wall Gun Locks.) I personally tried many types of flint over the years, but have always found the English Black Flints work best for me.
Gus