CDG Diamond Cutting & Polishing Standards 3 — Questions and Answers
Question 1: When evaluating a round brilliant for symmetry, a grader notes that opposite facets are not the same size. What symmetry feature is being described?
- Off-center culet
- Wavy girdle
- Facets out of alignment
- Upper and lower half facets of unequal size or shape (Correct answer)
Correct answer: Upper and lower half facets of unequal size or shape
Unequal upper-half or lower-half facets means paired facets on opposite sides of the diamond differ in size or shape, disrupting rotational symmetry.
Question 2: Which term describes the optical phenomenon where a well-cut diamond displays alternating dark and light patterns that create a three-dimensional pinwheel effect?
- Scintillation
- Contrast patterning (Hearts and Arrows effect) (Correct answer)
- Fluorescence haloing
- Dispersion banding
Correct answer: Contrast patterning (Hearts and Arrows effect)
Contrast patterning—most famously the Hearts and Arrows effect—arises from precise optical symmetry, creating a pinwheel of alternating bright and dark zones visible in a reflector scope.
Question 3: A diamond's 'spread' refers to which measurement characteristic?
- The distance from table to culet along the vertical axis
- The face-up diameter relative to the stone's carat weight, indicating how large a diamond appears per carat (Correct answer)
- The width of each individual girdle facet
- The angular difference between crown and pavilion
Correct answer: The face-up diameter relative to the stone's carat weight, indicating how large a diamond appears per carat
Spread describes how large a diamond looks face-up for its weight; a diamond with good spread appears larger than average for its carat weight.
Question 4: In laser cutting technology used for diamonds, what type of laser is most commonly employed?
- Carbon dioxide (CO₂) laser
- Nd:YAG (neodymium-doped yttrium aluminum garnet) laser (Correct answer)
- Excimer laser
- Diode laser
Correct answer: Nd:YAG (neodymium-doped yttrium aluminum garnet) laser
Nd:YAG lasers operating in the infrared range are the standard tool for sawing and drilling diamonds because their wavelength is efficiently absorbed by the carbon lattice.
Question 5: Which gemological term describes a cutting style that features concentric rows of rectangular or square facets, with no upper-half or lower-half facets?
- Brilliant cut
- Step cut (Correct answer)
- Mixed cut
- Rose cut
Correct answer: Step cut
Step cuts, such as emerald and Asscher cuts, have parallel rows of trapezoidal or rectangular facets arranged in tiers, emphasizing clarity over brilliance.
Question 6: A GIA grader marks 'paint' as a clarity characteristic on a diamond plot. What does this indicate?
- An internal graining pattern
- A surface coating or residue left from the polishing compound that appears as a thin film (Correct answer)
- A series of pinpoints in a cloud formation
- An indented natural on the girdle
Correct answer: A surface coating or residue left from the polishing compound that appears as a thin film
Paint refers to a thin layer of polishing residue or boric acid compound remaining on the surface, creating a slightly hazy or greasy appearance that can be cleaned off.
Question 7: When a cutter must choose between two sawing planes for a piece of rough containing a large inclusion, which principle generally guides the decision?
- Always saw perpendicular to the octahedral crystal face regardless of inclusion location
- Position the inclusion so it falls in the saw kerf and is eliminated rather than retained in either polished stone (Correct answer)
- Saw along the cleavage plane nearest the girdle
- Choose the plane that yields the smallest finished stone to minimize cost
Correct answer: Position the inclusion so it falls in the saw kerf and is eliminated rather than retained in either polished stone
The cutter plans the saw cut to bisect and remove a large inclusion, ensuring neither finished stone retains the defect and maximizing the value of both resulting pieces.
CDG Diamond Cutting & Polishing Standards 3
When evaluating a round brilliant for symmetry, a grader notes that opposite facets are not the same size.
What symmetry feature is being described?