Turquoise is a semi-transparent to opaque stone that ranges in color from whitish blue to deep dark blue, and from deep dark green to a yellowish green.
Traditionally, it was said that the most prized turquoise color was a medium robin’s egg blue. Turquoise in its purest form is a hydrous phosphate compound of aluminum and copper, which creates the medium blue color we all know. Persian and Egyptian collectors prefer this medium blue color. Many say that this color is the most valuable because it is the purest, only having traces of copper or aluminum. However, other natural earth metals can be part of the chemical compound. Zinc and iron can create variations of turquoise called Faustite. Traces of these other metals cause the turquoise to gain a more greenish hue. This is argued to be more valuable because it is rarer in nature for this to happen. Many American collectors like the darker blues and greens. There is also a following of collectors who love the white turquoise. When shopping for turquoise stones or turquoise jewelry, don’t let the hype have too much influence on your decision, and keep your own personal taste in mind. The rule of thumb when technically measuring the value of turquoise is: the more dark and intense and clear the color, the is the more valuable the stone is.
How Color Influences The Value of Turquoise
It is generally accepted that a rich, even color is more valuable. The Turquoise Quality Index (or TQI) is a turquoise pricing system that takes two factors into consideration when determining a stone’s price value; Intensity and Transition. The TQI score is very dependent of the rarity. The rarer the stone’s color, the more valuable the stone. TQI color grading is done on a scale from 1 to 10. A score of a 1 being the lowest and 10 being the highest. Synthetic stones are always given a 1. Stones that have been artificially dyed never receive higher than a 2. Natural stones are examined more closely. The score for natural stones is 1 + (intensity) + (transition).
Synthetic = 1
Dyed = 2
Natural = 1 + Intensity + Transition
|dull, cloudy/harsh transitions
|limited expression of color, imperfections in color transitions
|Dark color, smooth color transitions
|Rich color, smooth color transitions
|1 to 20
Grading Turquoise Color Intensity
Intensity is how rich and dark the color is. There is a range of intensity from white to pales to medium to rich. As a rule of thumb, the richer and darker the color the rarer and therefore more valuable it is. A few exceptions contradict this rule. It is rare to find white turquoise and it is valued more than some of the slightly blue pale variations and there are hues of turquoise that are unique and score highly. When dealing with multiple colors, always go by the lower scoring color found on the stone.
White stones: +3
Pale stones: +1
Light colors: +2
Medium colors: +3-4
Rich colors: +5
Dark colors: +4
Grading Turquoise Color Consistency
Another factor of a color is the consistency of the coloration and transition between colors. In needs to be reinforced that this is just an evaluation of the changing of the color of the turquoise not the turquoise to matrix which is a completely different material. A stone’s color transitions can happen for many reasons. The natural chemical composition of the host rock turquoise was formed on can influence the way the turquoise color is presented. Sometimes the stabilization process can leave hash ugly scars on the stone. Sharp and harsh color transitions are not as valuable as smoother even turquoise color transitions. When dealing with multiple color transitions, always score by the lower scoring element found on the stone.
Obviously harsh transitions: +1
Sharp color, inconsistent color transitions: +2
Minor transition imperfections: +3
Smooth color transitions: +4
Perfectly uniform color : +5
Examples of Grading Turquoise Color