Roman Lycurgus Cup is a 1,600-year-old jade green Roman chalice. When you put a source of the light inside it it magically changes colour. It appears jade green when lit from the front but blood-red when lit from behind or inside. Now we know that romans dissolve silver and gold particles into the glass. These particles are 50 nanometers wide, less than one-thousandth the size of a grain of table salt.