182 Purple hued panes of Luxfer glass in a leaded glass sash. "Luxfer is the best known name in prism glass" in the late 19th and early 20th centuries. The horizontal prisms on the back side of the square tiles redirect sunlight from windows to deeper inside rooms. The purple tint comes from sunlight hitting the magnesium or manganese that is included in the glass making process. I note one cracked pane.