The GIA grading system evaluates gem color based on three components:
- Hue: This reflects the basic colors we perceive. When discussing a gem’s “color,” most people refer to its hue.
- Tone: This indicates a gem’s relative lightness or darkness on a scale from 2 to 8.
- Saturation: This describes the hue’s intensity on a scale from 1 to 6.
For instance, a tanzanite graded as “vB 6/6” means:
- Hue: Violetish-Blue (vB) – Blue dominant, violet secondary - more than 50% blue under white light.
- Tone: 6 – Medium Dark
- Saturation: 6 – Vivid
HUE – Blue or Violet Dominant?
“Blue dominant” (vB) means the stone appears more than 50% blue when viewed under white light.
Even in blue-dominant tanzanite, flashes of violet are still visible due to its natural pleochroism.
In gemological reports, color is written using abbreviations: the primary color is capitalized, and the secondary color is lowercase.
For example:
- vB = violetish blue
- bV = bluish violet
Important Facts
It’s important to note that the GIA does not issue Gemological Reports stating a tanzanite’s color grade. They simply state if the stone is blue or violet dominant.
Lighting Matters
Tanzanite is graded under ONLY white light. Your stone WILL change color under different lighting conditions – and some stones can be very “moody” or exhibit very different colors in different lights. Yellow light makes your stone more violet , and white light more blue.
Buyer beware! If you're looking for (or have been promised) an intensely saturated blue tanzanite weighing less than 2.50 carats with a vb 6/6, you may be in for a disappointment. A fine, 1.00-carat tanzanite is likely to be at most a medium blue, or GIA 5/5. Be cautious of online retailers selling smaller stones (between 0.50 and 2.50 carats) as “investment grade” or GIA 6/6 !
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