CGC CGC Gemstone Treatments & Enhancements 2

Question 1

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

Accepted Answer

Blue topaz

Answer

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?

Accepted Answer

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

Answer

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?

Accepted Answer

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

Answer

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?

Accepted Answer

HPHT treatment

Answer

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?

Accepted Answer

To create channels to remove or bleach dark inclusions

Answer

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

CGC - Certified Gemstone Consultant Practice Test

CGC - Certified Gemstone Consultant Practice Test

CGC CGC Gemstone Treatments & Enhancements 2