Nevada Backroaders

Here's some details about sun purple glass, which we sometimes find at old mine sites. I plagiarized this from the internet:

"Beginning in the 1860's, glass makers in the United States started using manganese to give glass clarity instead of lead due to lead shortages created by the Civil War. Glass containing manganese eventually turns a light purple when exposed to sunlight, a side effect that was unknown at the time that this practice started. By roughly 1915, most companies in the United States switched from manganese to selenium to maintain clearness in their glass. Thus, with a few exceptions, including Heisey, Fostoria and Imperial, companies that produced this type of glass likely manufactured it from the 1860's to the years around 1915."

I also discovered that the glass can turn purple fairly quickly, in just a few months.

In fact, many antique dealers have been purposefully turning their old glass purple, either by putting it in the sun, or accelerating the process using strong UV lamps. It proves that the glass is old, and people assume that the purple color makes it more valuable. In fact, so much old glass has been turned purple that it's hard to find glass from that era that isn't purple. And so, non-purple glass from that era is actually more valuable than the purple stuff. Glass experts actually consider purpled glass items to be "ruined".