Researchers have demonstrated an idea for an invisibility cloak using calcite, a common crystalline material.

Cloaking relies on guiding light waves such that waves from a hidden object do not reach the eye.

Calcite accomplishes this by sending the two "polarisations" of light - directions in which the light waves oscillate - in different directions.

The work in Nature Communications can hide centimetre-sized objects, limited only by the calcite crystal's size.

The approach offers a simpler, more scalable route to invisibility than prior approaches.
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http://www.bbc.co.uk/news/science-environment-12338447



Cloaks of invisibility are relatively rare in folklore; although they do occur in some fairy tales, such as The Twelve Dancing Princesses, a more common trope is the cap of invisibility.[1] The cap of invisibility has appeared in Greek myth: Hades was ascribed possession of a cap or helmet that made the wearer invisible.[2] In some versions of the Perseus myth, Perseus borrows this cap from the goddess Athena and uses it to sneak up on the sleeping Medusa when he kills her. A similar helmet, the Tarnhelm, is found in Norse mythology. In the Second Branch of the Mabinogi, one of the important texts of Welsh mythology, Caswallawn (the historical Cassivellaunus) murders Caradog ap Bran and other chieftains left in charge of Britain while wearing a cloak of invisibility
http://en.wikipedia.org/wiki/Cloak_of_invisibility