DCA Laboratory Testing & Equipment 3

Question 1

Which gemological microscope illumination technique is best for observing surface blemishes such as scratches and polish lines?

Accepted Answer

Oblique illumination

Answer

Oblique (or side) illumination rakes light across the surface at a low angle, making surface irregularities highly visible by casting micro-shadows.

Question 2

What is the primary advantage of using immersion in a liquid-filled cell when examining a diamond under a microscope?

Accepted Answer

It reduces surface reflections and improves clarity observation

Answer

Immersion in a liquid with a refractive index close to the stone's reduces internal reflections, making it easier to observe internal features.

Question 3

An FTIR (Fourier Transform Infrared) spectrometer is most useful for identifying diamonds because it can:

Accepted Answer

Detect nitrogen aggregation patterns to classify diamond type

Answer

FTIR analysis reveals how nitrogen atoms are arranged (Type Ia, Ib, IIa, IIb), which also helps identify treatments and synthetics.

Question 4

Cathodoluminescence (CL) imaging helps gemologists identify HPHT-treated diamonds because treated stones often show:

Accepted Answer

Unusual growth sector patterns different from natural diamonds

Answer

HPHT treatment alters the diamond's lattice strain and growth sectors, producing distinctive CL patterns not seen in untreated natural diamonds.

Question 5

Which statement about using a refractometer to test a mounted diamond is correct?

Accepted Answer

It cannot be used because diamond's RI exceeds the instrument's range

Answer

Diamond's refractive index (~2.42) exceeds the upper limit (~1.81) of standard gemological refractometers, so no reading is obtainable.

(DCA) Certified Diamond Council of America Diamond Specialist Practice Test