Roman Lycurgus Cup (4th-5th Century CE), a jade green Roman Chalice.
When you put a source of light inside, it magically changes colour. It appears jade green when lit from front but blood-red when lit from behind or inside.
Now we know that romans dissolve silver and gold particles into glass. These particles are 50 nanometers wide, less than 1000th size of a grain of table salt.
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