Purple glass was manufactured between 1880 and 1914. The manufacturing process included the addition of manganese to produce clear glass. However when this glass was exposed to the ultra-violet rays of the sun, it turned to an amethyst color. This process was used until 1914 when World War I cut off the supply of manganese from Germany. Most of my pieces are a light amethyst, but some can achieve a deep purple color depending on how much manganese was added to a particular batch.
I'm not sure if I exposed my pieces to the sun if they'd darken. Hmmm...maybe I'll try it with one of the smaller ones.
We had a wonderful visit with Mom & Dad. I'm so glad that they were able to come visit...even if it did take them two days to drive across Texas. They didn't go home that way, however.