The bump was enshrouded in a layer of photonic crystals that bend light waves. The process distorted the ability of the bump to reflect light itself, and thus it became invisible!
Scientists feel that though the experiment was small-scale, it can theoretically be replicated at any size. However, the amount of time to create even a human-sized cloak would be, at this point, prohibitive. So, dashing hopes for Star Trek–like advances, there will be no Romulan or Klingon cloaking devices for the moment (Kate Kelland, "A Real Life 3D Invisibility Cloak? Scientists Make Gold Disappear," Reuters, March 20, 2010).