(This takes a bit of practice, obviously.). The first glass window panes were made in the Middle Ages. The most common method was to blow liquid glass into a disc, which could then be cut and flattened into panes. Windows were made in this way until the 1800s, when a method of making glass in plates was invented. Soon ordinary people were able to look out of the window and keep out the rain at the same time. People in glass houses shouldn’t throw stones.