Q: You mentioned that old glass bottles and insulators and even pressed glass goblets may turn purple if left in the sun a long time. Why?
A: We learned from an article in Antique Bottle & Glass Collector magazine that coloring changes in glass are caused by chemicals in the glass. Arsenic was used in glassmaking before World War II, and when left in the sun that glass turns yellow. Manganese was used before 1930, and that glass turns pale purple in sunlight. The very dark purple bottles seen at flea markets today are irradiated with modern machines, not by the slow rays of the sun.