Gemology Certification Gemstone Cutting & Lapidary Arts 2 — Questions and Answers
Question 1: What is the primary purpose of preforming during the gemstone cutting process?
- Shaping the rough into an approximate final outline before faceting (Correct answer)
- Polishing the final facets to a mirror finish
- Drilling holes through beads
- Orienting the rough for color or optical axis
Correct answer: Shaping the rough into an approximate final outline before faceting
Preforming shapes the rough gem into a basic outline (dome, cone, or disc) that closely approximates the finished shape before individual facets are cut.
Question 2: Which lapidary technique is used to create a dome-shaped, unfaceted gemstone surface?
- Cabochon cutting (Correct answer)
- Faceting
- Carving
- Bruting
Correct answer: Cabochon cutting
Cabochon cutting grinds and polishes a stone into a smooth, convex dome on top with a flat or slightly curved base, used for opaque or phenomenal gems.
Question 3: What is 'bruting' in diamond cutting?
- Rounding the diamond's girdle by spinning two diamonds against each other (Correct answer)
- Polishing the table facet to mirror finish
- Splitting the diamond along its cleavage plane
- Applying the first pavilion facets
Correct answer: Rounding the diamond's girdle by spinning two diamonds against each other
Bruting (girdling) creates a round girdle outline by spinning two mounted diamonds against each other on a lathe, shaping the rough into a round profile.
Question 4: When orienting a ruby before cutting, which optical axis direction maximizes the appearance of the red color?
- Table perpendicular to the c-axis so the c-axis runs through the girdle (Correct answer)
- Table parallel to the c-axis
- Table at 45° to the c-axis
- Orientation has no effect on color in corundum
Correct answer: Table perpendicular to the c-axis so the c-axis runs through the girdle
In ruby (trigonal corundum), orienting the table perpendicular to the c-axis makes the red ordinary ray dominate the face-up appearance, intensifying the red color.
Question 5: What grinding medium is most commonly used on a lapidary wheel to shape gemstones harder than quartz?
- Diamond abrasive (Correct answer)
- Silicon carbide
- Aluminum oxide
- Cerium oxide
Correct answer: Diamond abrasive
Diamond abrasive wheels (sintered or electroplated) are used for shaping hard gemstones because diamond is the hardest known natural material at 10 on the Mohs scale.
Question 6: What is the meaning of the term 'extinction' as used in gemstone cutting evaluation?
- Dark areas in a faceted stone where no light is reflected back to the viewer (Correct answer)
- The complete loss of fluorescence under UV light
- The fading of color in a gem over time
- The inability to see inclusions under magnification
Correct answer: Dark areas in a faceted stone where no light is reflected back to the viewer
Extinction refers to dark zones visible in a faceted gemstone face-up where light exits through the pavilion instead of reflecting back, typically caused by steep pavilion angles or poor cutting.
Gemology Certification Gemstone Cutting & Lapidary Arts 2
What is the primary purpose of preforming during the gemstone cutting process?