Scientists reproduce ancient Roman colour-changing glass technique

Scientists have worked out how Roman craftsmen made glass that changes colour, copying a technique lost for over a thousand years. The object at the centre of this discovery is the Lycurgus Cup, a Roman cup that is about 1,600 years old. The cup looks jade green in normal light, but turns ruby red when light shines through it from behind. Scientists found that the Romans mixed tiny gold particles into the glass to create this effect. The gold was heated until it turned to vapour, and then it stuck to the glass. Researchers have now reproduced this process successfully in a modern setting. The discovery shows that Roman glassmakers had a surprisingly advanced understanding of materials, even without modern scientific knowledge.