What does surface modification involve?

Surface modification refers to techniques that alter a gem's appearance without changing its fundamental structure. This primarily involves using backings or coatings to enhance visual traits such as color and shine. The use of backings can give a stone a more vibrant look or improve its depth of color by reflecting light in specific ways. Coatings can also be applied to create specific finishes or effects, such as a more intense hue or added luster.

Techniques like applying heat are categorized under treatment rather than surface modification because they fundamentally affect the gem's properties rather than just its surface appearance. Cutting impacts clarity, which is a significant aspect of gem quality but is not a surface modification. Extracting impurities, although it may make a gem look cleaner, does not fit the definition of surface modification since it involves alteration beyond the surface level. Thus, changing a gem's appearance through backings or coatings accurately encompasses what surface modification entails.