For centuries, the only way to get purple dye in Europe was by harvesting tens of thousands of murex snails from the ocean. TIL the Mayans discovered this independently
Dyes — MayaIncaAztec.com
https://www.mayaincaaztec.com/mia-similarities/dyes
All three, the Maya, Inca, and Aztec used the tiny coccid insect to produce the brilliant color of crimson. This color dye, which is called cochineal, became an important trade item between the New World and Europe. It became so valuable in the New World that only gold and silver were worth more. Th
They also produced the color purple or lavender from the murex mollusks that were found on the seacoast. Dye makers rubbed two of the mollusks together in order to extract the dye.
That sounds simple enough, but it also involved some real chemistry:
https://hal.science/hal-03202592/document
Purple was one of the most expensive and difficult dyes to acquire and process. 1 gram takes 10,000 snails. In Europe, it was solely used for kings.
This feels like a dumb question, but I'll ask it anyway - Why not just mix red & blue dyes?
I don't really have great knowledge on this topic but my understanding is that it wasn't just because it was purple, it was that the resulting purple dye was excellent; it was bright, beautiful and never faded. You can dye stuff purple with cabbage but it's just not a very good dye in those regards
I think it's because the colours are generated by a chemical reaction from e.g. woad (-> blue) or madder (-> red) which happen under different conditions.