Many earlier cloaking systems turned objects "invisible" only under wavelengths of light that the human eye can't see. Others could conceal only microscopic objects. (See "Two New Cloaking Devices Close In on True Invisibility.")

But the new system, developed at Massachusetts Institute of Technology and the Singapore-MIT Alliance for Research and Technology (SMART) Centre, works in visible light and can hide objects big enough to see with the naked eye.

The "cloak" is made from two pieces of calcite crystal—a cheap, easily obtained mineral—stuck together in a certain configuration.

Calcite is highly anisotropic, which means that light coming from one side will