Last Updated: Dec 09, 2016     Views: 1271

Most colored glasses are stable in sunlight.

There are some special glasses that react to sunlight (UV). I've listed several examples. However, in these cases, sunlight adds color, rather than bleaching the glass.

1) Some glasses "solarize" or change from colorless, transparent glass to purple or other colors. This process is called "solarization."

From The Corning Museum of Glass website Glass Resources / Resource on Glass / Solarized Glass

"Certain types of colorless, transparent glasses, when exposed to sunlight for extended periods of time, develop a pink or pale purplish color. Bottles, insulators, and other objects having their color changed in this way are often called "desert glass," but the scientist prefers the term "solarized glass." Other well-known examples are the famous purplish windows on Beacon Street in Boston and the little circular glass disks sometimes found in sidewalks of older parts of cities. Occasional examples of solarized glass are also found from the ancient world."

For another version:

and from eBay:

In this article, "Action of Sunlight on Glass" from Popular Science Monthly, volume 5, May 1874, E. S. Drone observes the changes in the color of historical glass due to sunlight:

2) Photosensitive glasses, made from noble metals, were developed by Dalton and later Stookey, at Corning Glass Works/Corning Inc, during the Second World War (and kept under wraps by the US government until the war ended). They were never much exploited by Corning until the 1950s and 1960s when they were offered as a novelty glass.

Gaffer Glass has reintroduced these types of glasses. This type of photosensitive glass must be exposed to an ultraviolet light in the finished piece and then exposed to heat for 3-4 hours to change the colors.

In general, it is best to keep glass out of sunlight. The heat produced by the sun may cause glass to break.