inspection. Those that do not have a visible inclusion when the gem is examined approximately 6 inches from the naked eye are known as "eye-clean", although visible inclusions can sometimes be hidden under the setting in a piece of jewelry. The most expensive gem diamonds fall within the VS and SI grades with FL, IF, and even VVS stones commanding significant premiums. FL and IF stones are sometimes referred to as "museum quality" or "investment grade" to denote their rarity although the term "investment grade" is misleading as diamonds have historically been illiquid and questionable stores of value. Clarity enhancement Laser "drilling" involves using a laser to burn a hole to a colored inclusion, followed by acid washing to remove the coloring agent. The clarity grade is the grade after the treatment. The treatment is considered permanent. Clarity can also be "enhanced" by filling the fracture much like a car windshield crack can be treated. Such diamonds are sometimes called "fracture filled diamonds". Reputable vendors must disclose this filling and reputable filling companies use filling agents which show a flash of color, commonly orange or pink, when viewed closely. There is a significant price discount for fracture-filled diamonds. The GIA will not grade fracture-filled diamonds, in part because the treatment is not as permanent as the diamond itself. Reputable companies often provide for repeat treatments if heat causes damage to the filling. The heat required to cause damage is that of a blowtorch used to work on settings, and it is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can apply cooling agents to the diamond and use greater care while working on it. GIA, as a matter of policy, does not grade clarity-enhanced diamonds but it will grade laser-drilled diamonds since it considers the enhancement to be permanent in nature. If a GIA report has the words "clarity enhanced" or "fracture filled", it is surely a counterfeit report. See also Diamond Diamond color Diamond enhancement List of diamonds Synthetic diamond References Diamond Quality