Gemstone Grading & Evaluation Flashcards

In the GIA colored stone grading system, which three components together describe a gem's color?

Answer: Hue, tone, and saturation

GIA describes colored stone color by hue (basic color), tone (lightness/darkness), and saturation (intensity).

Which lighting condition is generally recommended when grading the color of colored gemstones?

Answer: Daylight-equivalent fluorescent light around 5500–6500K

Daylight-equivalent lighting provides a neutral, consistent standard for color comparison.

A grader notes a brownish saturation modifier on a stone. In which hue is a brownish (rather than grayish) modifier expected?

Answer: Orange spessartine garnet

Warm hues such as red, orange, and yellow show brownish modifiers, while cool hues show grayish ones.

A light, washed-out area in the center of a faceted stone through which you can read print is called what?

Answer: Windowing

A window results from a shallow pavilion that lets light pass straight through instead of reflecting back.

Dark areas in a face-up colored stone that reduce its brightness are referred to as:

Answer: Extinction

Extinction describes dark areas caused by light leaking out or being blocked, often from a deep pavilion.

For most colored gemstones, which tone range is typically most valued in the market?

Answer: Medium to medium-dark

Medium to medium-dark tones usually allow the strongest saturation and are most prized.

A sapphire rough shows strong color zoning. How does a cutter usually orient the stone to give the best face-up color?

Answer: With the colored zone placed near the culet so it spreads color throughout

Placing the color zone near the pavilion bottom lets reflections distribute color evenly face-up.