The shine that the viewer sees on viewing a Gemstone is known as luster. It is dependent on number of factors including:

1. The hardness of the Gemstone.
2. The evenness of the outer and inner texture of the Gemstone.
3. In transparent Gemstones the flawlessness of the inner part of the Gemstone.
4. The quality of the Gem material.
5. The expertise of the Gem Cutter.