The 3D-printed goblet is dichroic, meaning it changes colour under different light. The team used a method for producing gold nanoparticles to make larger, elongated nanoparticles with dichroic properties. They combined this with 3D printing materials, polyvinyl alcohol (PVA), to make an ink that could be used to print objects with vivid colours. When light is shone through the cup it looks purple because electrons on the surface of the gold nanoparticles absorb light of certain wavelengths. The 3D-printed goblet is dichroic, meaning it changes colour under different light.

Source: Daily Mail March 01, 2019 18:00 UTC