EC , I read so much stuff that I could well have imagined it, especially as my brain cells are deteriorating at a rapid rate these days! In that case I must apologise for talking rubbish
I can't remember where I saw this originally,but there is a bit
here (pg 94) about the making of glass in the Rhineland and Normandy in the early medieval period.
Also this mention here
"Up north, in the colder climates, Germanic tribes could have used these sheets of glass, but it took hundreds of years before they actually adapted glassmaking to their needs. In the Middle Ages, around 600 A.D., the Germans established window manufacturing plants along the Rhine River.
Good glassmakers were few and far between at that time. It took a great amount of skill and a long apprenticeship before a man was qualified to do the job properly. That’s why they called a glassmaker a “gaffer” – German for “learned grandfather”.
Glassmaking in those days was done in two ways. The method that was most widely used, but produced inferior-quality glass, was called the cylinder method, where the glassmaker blew molten silica into a sphere and swung it back and forth until it was shaped like a cylinder. Then they cut the cylinder lengthwise and flattened it into a sheet."
The other method, called the crown method, was a specialty among Normandy glassmakers. These craftsmen also blew a sphere, but attached an iron rod to it before cracking off the blowing iron, leaving a hole at one end. Then they’d rapidly rotate the sphere, using centrifugal force to expand the hole until the sphere opened into a disk. Crown glass was thinner than cylinder glass and could only be used for very small window panes.
Full article
But I have to agree that neither of these two articles give specific dates.
Norman glass didn't become well-known until later. There's an interesting theory that glassmaking in Normandy really took off with the aid of Jewish artisans.
"It became evident that the only reasonable manner in which the art could have appeared in Normandy and Piedmont was by relocating glassmakers from Palestine to Europe.
This process was not unprecedented. It was an already documented fact in Christian annals that the Norman Crusader, Roger II, after invading Byzantium, took its most valuable treasure, the Judaic silkmakers of Thessalonica and Thebes to Sicily, then under Norman rule. The art of glassmaking likewise appeared in Sicily and Normandy during that period. The connection between the Norman Crusaders and the appearance of the art of glassmaking in Norman territories was evident."
http://www.hebrewhistory.info/factpaper ... altare.htm
(I was joking about the plate glass
)
). I'm pretty sure such a large expanse of glass would not have been used in a building until, perhaps, Victorian times with that exposition center (you Brits will have to remind me what it's called), which absolutely awed people when it was built some eight centuries after the Conquest. 
