GIA Laboratory Testing & Equipment 2 — Questions and Answers
Question 1: Which instrument uses a diffraction grating to separate light into its spectral components for diamond testing?
- Refractometer
- Spectroscope (Correct answer)
- Polariscope
- Dichroscope
Correct answer: Spectroscope
A spectroscope separates light using a diffraction grating or prism to reveal absorption lines that help identify gemstones.
Question 2: When using a thermal conductivity probe on a diamond, what does a high reading indicate?
- The stone is glass
- The stone is moissanite
- The stone is a genuine diamond or moissanite (Correct answer)
- The stone is cubic zirconia
Correct answer: The stone is a genuine diamond or moissanite
Diamonds and moissanite both conduct heat rapidly, causing a high thermal conductivity reading, so a secondary test is needed to distinguish them.
Question 3: What is the primary function of a Chelsea color filter when examining diamonds?
- Detect fluorescence
- Separate colored stones from colorless diamonds (Correct answer)
- Reveal inclusions
- Measure refractive index
Correct answer: Separate colored stones from colorless diamonds
The Chelsea filter transmits red and yellow-green light, helping distinguish certain colored stones, though it has limited use with colorless diamonds.
Question 4: In spectroscopy, the Cape series absorption lines in natural diamonds appear at which wavelength range?
- 700–750 nm
- 415–478 nm (Correct answer)
- 500–550 nm
- 600–650 nm
Correct answer: 415–478 nm
Cape series diamonds show a characteristic absorption line at 415 nm (and sometimes 452 nm and 478 nm) due to nitrogen aggregates.
Question 5: Which type of microscope stage is most useful when examining a diamond for strain patterns?
- Dark-field stage
- Polarized light stage (Correct answer)
- Bright-field stage
- UV fluorescence stage
Correct answer: Polarized light stage
A polarized light stage reveals anomalous birefringence and strain patterns that can help identify certain diamond treatments or synthetic origins.
Question 6: What does FTIR spectroscopy primarily measure in diamond samples?
- Color saturation
- Absorption of infrared radiation (Correct answer)
- UV fluorescence intensity
- Specific gravity
Correct answer: Absorption of infrared radiation
FTIR (Fourier Transform Infrared Spectroscopy) measures how a diamond absorbs infrared radiation, revealing nitrogen content and type classification.
Question 7: When calibrating a refractometer for gemological use, which liquid is placed on the hemispherical glass?
- Distilled water
- Methylene iodide
- Contact liquid with refractive index ~1.81 (Correct answer)
- Immersion oil with RI 1.515
Correct answer: Contact liquid with refractive index ~1.81
A contact liquid with an RI of approximately 1.81 is used to ensure optical contact between the stone and the refractometer's glass hemisphere.
GIA Laboratory Testing & Equipment 2
Which instrument uses a diffraction grating to separate light into its spectral components for diamond testing?