Paul , there used to be alot of glass factory around in these small towns an the way I understand it at the end of a shift or maybe a glass run they swung the pipe or spout away an it dripped a big ole chunk of glass out. Before my time so I can,t say for sure but I have seen globs of glass that is amber an also a green insulator color, I,ll see if I can get a picture of the big chunk that I acquired from a friend of mine, makes nice points but will cut the crap out of ya workin it. We also have alot of factory glass that was used in the steel mills I believe. Anyways we find alot of it when we do excavation for new projects in the city. Most of it has a lot of impurtys or slag in it an isn,t as nice a glass factory stuff. Hope this helps as I don't know to much about these materials. Bob