Crystals formed by breathing on a window. Hidden beauties of nature. 1900.

Roman Glass Window-Pane, 1st-2nd Century CE, Garden Hill, Hartfield, Sussex, The British Museum, London

Although not all windows were glazed, small fragments of window- glass are found on many Roman sites. Almost complete panes, like this one from a bath-house, very rarely survive. It belongs to the earlier Roman type made by casting a flat sheet of glass in a stone or wooden tray and cutting smaller panes from it as required.