On Beacon Hill in Boston there are some very old houses and some of the window panes, original to the house, have turned a delicate lilac from sun .... and owners are very proud of them. They go to great pains (groan) to protect and care for them.

There is an old saying about glass and its fluidity when heated and its fusion as it cools :
"Any idiot can tie knots in glass but it takes a Master to untie them."
(neatly bringing thread back to the skill of glassblowers) {smug grin -e}