Glass making and glass working workshops were a separate thing back then, my question is what was the raw form of glass that glass working shops bought to melt into liquid and create bottles and stuff with. Was it small beads like raindrops or large square chunks of glass ? or maybe glass panes ? Also what were the units used for glass? I can't find anything about this topic all I find about glass are already made objects.
I can't imagine you would be trading to a different town in something already made like bottles just for it to be remelted.
The basic component of glass is sand. Melted sand could be formed into useful shapes by pouring. Add various chemicals to the melt created colors. Cobalt made glass blue, for example. The colored glass was used as decorations in Egyptian tombs and temples and jewelry. The development of the blowing techniques made it possible to produce bottles for storage of wine and alcohol beverages such as beer.