So how exactly did the Chinese stumble upon the intricate formula to make Han purple, which involved combining silica (sand) with copper and barium in precise proportions and heating to about 850-1000 °C? A team of Stanford physicists published a paper in the Journal of Archaeological Science ( summary here ), which proposes that Han purple was a by-product of the glass-making process, as both glass and the purple pigment contain silica and barium. Io9.com writes that barium makes glass shinier and cloudy, which means this pigment could be the work of early alchemists trying to synthesize white jade.