CGC CGC Gemstone Treatments & Enhancements 2 — Questions and Answers
Question 1: Which gemstone is most commonly irradiated to produce blue color in the U.S. market?
- Diamond
- Emerald
- Blue topaz (Correct answer)
- Sapphire
Correct 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.
Question 2: What care precaution must jewelers take when working on fracture-filled rubies?
- Avoid ultrasonic cleaning only
- Avoid all heat, acids, and ultrasonic cleaning to prevent damage to the filling (Correct answer)
- Only avoid steam cleaning
- No special precautions are needed
Correct 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.
Question 3: What does 'no evidence of heat treatment' on a GIA report indicate about a sapphire's value?
- The stone has lower value due to lack of processing
- The stone is likely more valuable as untreated stones command significant premiums (Correct answer)
- It means the stone is synthetic
- It has no effect on value
Correct 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.
Question 4: Which treatment is used on diamonds to remove or reduce yellowish color through high-pressure, high-temperature processing?
- Fracture filling
- Laser drilling
- HPHT treatment (Correct answer)
- Coating
Correct 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.
Question 5: What is 'laser drilling' used for in diamond treatment?
- To improve a diamond's cut proportions
- To create channels to remove or bleach dark inclusions (Correct answer)
- To add color to colorless diamonds
- To increase carat weight
Correct 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.
Question 6: Which coating treatment is sometimes applied to enhance or change a gemstone's apparent color?
- Flux healing
- Surface coating with metallic oxides or foil backing (Correct answer)
- Irradiation coating
- Wax impregnation
Correct 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.
CGC CGC Gemstone Treatments & Enhancements 2
Which gemstone is most commonly irradiated to produce blue color in the U.S. market?