CGA Gemstone Treatments & Enhancements 2 — Questions and Answers
Question 1: Tanzanite is almost universally heat-treated before sale. What color change does this treatment produce?
- Purple to colorless
- Green to blue-violet
- Brown to blue-violet (Correct answer)
- Yellow to orange
Correct answer: Brown to blue-violet
Naturally mined tanzanite is typically a brownish or trichroic stone; heat treatment at relatively low temperatures eliminates the brown component and intensifies the prized blue-violet color.
Question 2: Traditional surface (lattice) diffusion treatment of sapphires is distinguished from beryllium diffusion primarily because it:
- Penetrates the entire stone uniformly
- Affects only a thin surface layer (Correct answer)
- Uses a different element but penetrates deeply
- Does not alter color at all
Correct answer: Affects only a thin surface layer
Traditional surface diffusion uses titanium or chromium ions that penetrate only a thin surface layer, so recutting or repolishing often removes the color, unlike beryllium which diffuses much deeper.
Question 3: Laser drilling in diamonds is used by gem treaters primarily to:
- Inscribe identification numbers on the girdle
- Create decorative faceting patterns
- Access and improve the appearance of dark inclusions (Correct answer)
- Increase the diamond's refractive index
Correct answer: Access and improve the appearance of dark inclusions
A laser bores a tiny channel from the diamond's surface to a dark inclusion, allowing bleaching agents to lighten or remove it, which can improve the apparent clarity grade.
Question 4: A classic diagnostic feature of lead-glass fracture-filled diamonds is an iridescent color seen in fractures, called:
- Adularescence
- Flash effect (Correct answer)
- Chatoyancy
- Aventurescence
Correct answer: Flash effect
The flash effect — typically an orange-pink or blue-purple iridescent glow seen in fractures under the microscope — is a hallmark of lead-glass fillings caused by thin-film interference.
Question 5: Which specialized laboratory technique is the definitive method for detecting beryllium in diffusion-treated sapphires?
- Infrared spectroscopy (FTIR)
- Raman spectroscopy
- LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) (Correct answer)
- Energy-dispersive X-ray fluorescence (EDXRF)
Correct answer: LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry)
LA-ICP-MS is the only reliable method to detect the extremely low concentrations of beryllium introduced by diffusion treatment, as standard gemological instruments and even EDXRF lack the sensitivity required.
Question 6: When GIA issues a grading report for a clarity-enhanced diamond that has been laser drilled, how is the treatment disclosed?
- GIA refuses to issue reports for laser-drilled diamonds
- The treatment is noted in the clarity treatment section of the report (Correct answer)
- The diamond is graded identically to untreated stones with no notation
- Only a verbal disclosure to the submitter is made
Correct answer: The treatment is noted in the clarity treatment section of the report
GIA notes 'laser drilling' in the clarity enhancement section of its reports and may use a dashed plot symbol to indicate the drill channel on the diagram, ensuring buyers receive full disclosure.
Question 7: Which of the following gemstone treatments is generally considered permanent, stable, and widely accepted without special disclosure requirements in the corundum trade?
- Fracture filling with lead glass
- Low-temperature wax impregnation
- Moderate heat treatment of sapphires (Correct answer)
- Surface diffusion with titanium
Correct answer: Moderate heat treatment of sapphires
Moderate heat treatment of corundum has been practiced for centuries, produces stable and permanent results, and is so pervasive that many trade standards treat it differently from other enhancements, though disclosure is still recommended.
CGA Gemstone Treatments & Enhancements 2
Tanzanite is almost universally heat-treated before sale.
What color change does this treatment produce?