Purple beads are fairly rare in a large number of places, and they have been fairly rare for a long time. Even when looking at beads in a modern bead store, purple is not nearly as common as most other colors.
The primary reason for this is the difficulty in creating purple beads. In general, you can make purple glass by adding manganese as a colorant. Manganese is a very powerful colorant, though, and if you add too much, the glass turns such a deep purple as to appear black. Manganese can also be a fairly difficult mineral to get a hold of. The most common natural source of it is a mineral called wad, which encompasses things like pyrolusite and psilomelane.
Knowing which minerals glass makers used is difficult, though, given how much of the chemistry changes in the process of making the glass. Interestingly, wad is also used as a source of cobalt, depending on the type of wad. A number of the sources for wad in India, Africa, and parts of the Middle East seem to have been exploited for both colors. The Romans certainly seem to have used manganese to color large amounts of purple/violet glass. While the Romans seemed to like purple glass (and probably had the largest proportion of it compared to other regions), they didn’t seem to use it much for beads. So even though there’s a fair amount of purple glass, there still aren’t all that many purple beads.
Amethyst would be the primary material for purple stone beads. Amethyst can be found in Central Europe, South India, parts of East Asia, and southern Africa. While amethyst beads aren’t rare in many regions, I also wouldn’t call them common in most places.
Purple beads highlight the issue of getting your colors straight for chemistry reasons. Many purple glass beads are so dark they look black, but when you shine an LED light through, they can be anywhere from purple to hot pink. It’s always important to mention both colors. That way, the person reading the report understands the color people most likely viewed the bead as was black, but the chemical coloring of the bead is actually closer to purple.
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