CGC Gemstone Treatments & Enhancements Flashcards

Which gemstone is most commonly irradiated to produce blue color in the U.S. market?

Answer: Blue topaz

Blue topaz is almost universally irradiated and heat-treated to produce its blue color, as natural blue topaz is extremely rare; this treatment is standard and fully disclosed.

What care precaution must jewelers take when working on fracture-filled rubies?

Answer: Avoid all heat, acids, and ultrasonic cleaning to prevent damage to the filling

Lead-glass fracture-filled rubies are extremely sensitive to heat, acids, and ultrasonic vibration, all of which can damage or displace the filling material.

What does 'no evidence of heat treatment' on a GIA report indicate about a sapphire's value?

Answer: The stone is likely more valuable as untreated stones command significant premiums

A GIA 'no evidence of heat treatment' designation is highly desirable because unheated sapphires are rarer and command significant price premiums over heated stones.

Which treatment is used on diamonds to remove or reduce yellowish color through high-pressure, high-temperature processing?

Answer: HPHT treatment

HPHT (High Pressure, High Temperature) treatment can permanently improve a diamond's color grade by altering color-causing structural defects in the crystal.

What is 'laser drilling' used for in diamond treatment?

Answer: To create channels to remove or bleach dark inclusions

Laser drilling creates microscopic channels to reach dark inclusions, which are then dissolved or bleached with acid to improve the diamond's apparent clarity.

Which coating treatment is sometimes applied to enhance or change a gemstone's apparent color?

Answer: Surface coating with metallic oxides or foil backing

Thin coatings of metallic oxides or foil can be applied to gemstone surfaces or pavilions to alter apparent color, but these are not durable and must be fully disclosed.