Wow! So what are the distinct differences between glass of 1850 and 1860. Please enlighten me.
Also, when you mention the French heyday, you are I assume, referring to the Art Nouveau period of French glass such as Galle, Daum, Lalique and others of the period. This was and is now accepted as the top of French, (European), glass design but in terms of hand blown quality glass not the heyday.