When small, thin pieces of gem materials such as opal or shell are set into recesses within metal, the term inlay is used. Inlay opal generally uses smaller pieces of opal that are set with a black bonding agent to appear like black opal. They are, in effect, much like a let, with the jewelry itself becoming the backing. Inlay illustrates reasons #1, #2 and #3 for making assembled stones in that they allow use of small or thin pieces, which might otherwise be unsuitable for jewelry, lighter colored opal imitates the rarer black opal and the natural play of color is enhanced.