As you start doing work on restoring stained glass windows interesting things usually start popping up and the Lane Tech Clock Tower is not any different and is definitely providing us with an interesting item. Look at the picture of two full size glass windows in the tower. Take your time and scan back and forth between the two windows. What do you see? Not the broken and or missing pieces, but something else.
See it? The top picture is the West Face and the bottom picture is the North Face and it is the same glass. Notice how the West Face window has a violet tint and the North Face window is white. Both windows when they were installed were white and over the years the windows that got the most sun have turned a more violet color.
An interesting characteristic of some older glass is it contains manganese dioxide. Manganese has a tendency to turn different shades of purple or violet when exposed to the UV rays of the sun or to other ultra-violet sources. It is believed to be a photochemical reaction that is not completely comprehended. Generally it is accepted that the ultra-violet light initiates an electron exchange between the manganese and iron which, changes the manganese compound into a form that causes the glass to turn purple.