From Laughing Squid comes a report of an invention of a Rube Goldberg-type machine with “invisible glass”. Coolest thing I’ve seen today.

Youtube Video:

TL;DR: (spoiler): they use an oil that has the same refractive properties as glass to make the glass inserted in the oil to “disapear” – since they are the same refractive index, light does not bend around the glass, so no edges become visible. Pretty cool!