Refraction - the bending of light as it passes through a gemstone.
Relief - the contrast between the inclusion and the gemstone. A good example of this would be a lower clarity grade diamond that has eye visible inclusions (the internal characteristics).
Rhodium - is a metal in the platinum group. It is often used as a platinum alloy. Its purpose is to harden the platinum to give it greater durability for jewelry. The most common percentage mix of rhodium to platinum in jewelry is 95% platinum and 5 % rhodium. Also, rhodium is often used as a finishing plate or coating for white gold jewelry. It provides a non-tarnishing electroplate with high reflectivity. It gives the gold a high bright shine when polished.