Sure of school history course you remember that, often in peasant huts windows were made of bovine bladder due to lack of glass. Nevertheless, it's not that the glass in those days did not produce, and the difficulty in obtaining it and, consequently, expensive. The process of glass production and processing in those years was as follows. Glass melted in a bowl on an open fire. After receiving the frit (glass fragments) them in a special furnace. The temperature at the same time reaches 1500 degrees, which required a fair amount of firewood. In this case, and she could not stand long oven.
Drips out the same glass in the furnace, flushing with coal, it was impossible – because of the volatile fraction released during the burning glass, it acquired a distinct yellow color. As a result, for the glass, even a small amount was needed almost cubic meters of firewood, as well as mastery of "glazier" – the technology required extremely careful. It is evident that glass in those days was considered a luxury item. By the way, do not think that these times are long past. Back in the early 20th century in the Far East almost its weight in gold valued glass bottles, which served little currency for many hunters and fishermen of the locality. Technology of glass production and processing has since moved far ahead. Today it is no surprise even the furniture of glass, full glass shelves and tables. But even some 100 years ago on this was difficult to even contemplate.