DCA Laboratory Testing & Equipment 2 — Questions and Answers
Question 1: Which instrument uses ultraviolet light to reveal fluorescence characteristics in diamonds?
- Spectrophotometer
- UV lamp (longwave/shortwave) (Correct answer)
- Refractometer
- Polariscope
Correct answer: UV lamp (longwave/shortwave)
A UV lamp—available in longwave (365 nm) and shortwave (254 nm) versions—is the standard tool for observing fluorescence in diamonds.
Question 2: A DiamondView instrument is primarily used by gemological laboratories to:
- Measure refractive index precisely
- Distinguish natural diamonds from CVD and HPHT synthetics (Correct answer)
- Grade color on the D-to-Z scale
- Detect surface fractures under magnification
Correct answer: Distinguish natural diamonds from CVD and HPHT synthetics
The DiamondView uses short-wave UV to reveal growth patterns (cuboidal vs. triangular) that differentiate synthetic diamonds from naturals.
Question 3: When using a darkfield loupe, the illumination source is positioned so that light:
- Shines directly through the stone from below
- Enters from the sides so the background appears dark (Correct answer)
- Reflects off the table facet
- Passes through a polarizing filter first
Correct answer: Enters from the sides so the background appears dark
Darkfield illumination directs light from the sides, making the background dark and causing internal features to appear bright and visible.
Question 4: Which property does a thermal conductivity probe (diamond tester) measure to separate diamond from simulants?
- Electrical resistivity
- Heat dissipation rate (Correct answer)
- Refractive index
- Specific gravity
Correct answer: Heat dissipation rate
Diamond is an exceptional thermal conductor; the probe detects how rapidly heat transfers through the stone, distinguishing diamond from most simulants.
Question 5: A Presidium Duo tester adds electrical conductivity testing to thermal testing primarily to distinguish diamond from:
- Glass
- Cubic zirconia
- Moissanite (Correct answer)
- White topaz
Correct answer: Moissanite
Moissanite conducts heat similarly to diamond, but it also conducts electricity; the dual thermal/electrical test reliably separates the two.
Question 6: Specific gravity testing requires weighing a stone in air and then in water. Which formula is used?
- SG = Weight in water / (Weight in air − Weight in water)
- SG = Weight in air / (Weight in air − Weight in water) (Correct answer)
- SG = (Weight in air + Weight in water) / Weight in air
- SG = Weight in air × Weight in water
Correct answer: SG = Weight in air / (Weight in air − Weight in water)
SG equals the weight in air divided by the loss of weight in water (weight in air minus weight in water), per Archimedes' principle.
Question 7: When examining a diamond with a polariscope, a single-refracting (isotropic) stone displays:
- A banded interference figure
- Uniform darkness when rotated 360° (Correct answer)
- Four bright flashes of light per rotation
- A uniaxial optic figure
Correct answer: Uniform darkness when rotated 360°
Isotropic materials like diamond do not rotate polarized light, so the stone remains uniformly dark (extinct) as it is rotated between crossed polarizers.
DCA Laboratory Testing & Equipment 2
Which instrument uses ultraviolet light to reveal fluorescence characteristics in diamonds?