I've been off doing a bit of reading to double check my facts, as a number of things on the boards have caught my eye recently.
Argy Rousseau was born on the 17 March 1885 and was therefore not
active in the 1890's through to 1915.
His first exhibition showing glass was in 1914 at the Salon Des Artistes Francais. At that time he was a completely unknown glass artist. The majority of his pate de verre
was made through the 1920's, although work goes on to 1937.
I originally noticed this error in Andy McConnell's book on Twentieth Century Glass, published by Millers, back in late August when I bought a copy. I assume that is where you got your information, Stephen? In it Andy suggests that Argy Rousseau (amongst others) influenced Galle with work he exhibited at the 1878 Paris Exhibition - see page 71 under the title "Art Nouveau". This would not have been possible as he had not been born at the time
I thought I'd better check in case my memory was playing tricks before I made the post here to clarify a factual error
Interestingly, the illustrations in Andy's book both say "1925" and "1920".
The signatures were achieved by engraving the model before it was fired.