Oiling
oil·ing | ˈȯi(-ə)liŋ
verb
A temporary treatment used to enhance the color of a gemstone
Oiling is a technique used to enhance the appearance of a gemstone that has highly visible flaws or inclusions. The process involves filling the surface of a gemstone with a colorless material - usually oil or resin - to augment the appearance of the gem. This typically enhances the color but may have an impact on other elements of the gem, depending on the issues that are being addressed. Other substances may be used as well, though the process is designed not to be permanent, so glass or plastic is generally not used. By filling the cracks and fractures of a stone, oiling improves overall transparency in the gemstone temporarily.