Grading Saturation & Tone

Before determining the saturation and tone of the primary hue we first need to know where to look.

For a faceted gem, the true hue, saturation and tone will be seen in the areas of internal luster. Light entering the gem through the table or crown reflects off pavilion facets internally then returns to the eye.

Light entering the gem through a pavilion facet, reflects off the opposite pavilion facet and passes to the eye.

These areas of brilliance will seem to "change places" with complementary dark areas. Look for pinpoints of light or color or tiny areas of brilliant color.

Dark areas are often referred to as "extinction" and can be observed as the gem is "rocked" under a light source. Do not try to determing hue, saturation, and tone from the overall body color.

The areas of extinction result from light entering the gem through the table, crown, or pavilion and striking an internal facet at such an angle that the light does not return to the eye, resulting in dead or very dark areas.

Note: Extinction is often used in referring to large areas of a poorly cut gem that are permanently dark. While the characteristic is different, the physics of light is the same.

Color Satutation in Precious Gems

Imagine drops of blue ink being added to clear water.

Notice that the Hue is not actually changing. It is the same in each instance.

What is changing is the color saturation. In other words, the water is getting more oc the same color..

Each time ink is added, the saturation increases until it reaches maximum saturation. At 100% saturation, the water will have as much color as is possible

Tone in Precious Gems

Imagine the same drops of blue ink being added to highly saturated red water.

Notice that the Saturation is not changing.

It is the same in each instance.

Only the tone is growing darker with each drop of ink that is added.

However - while the concepts of saturation and tone are illustrated separately, they tend to be inseparable in observation.

Saturation simply means more of a color. Tone is the lightness or darkness caused by the saturation of the primary hue and additional hue components from other impurities.

The image below shows degrees of Saturation + Tone

Assigning a Composite Grade

First: Determine Saturation and Tone Grades

Saturation Grade

Tone Grade

Note: The saturation and tone swatches should only be considered to be guidelines

Then: Assign a Composite Grade by Using the Matrix
	Saturation Grade
Tone Grade		Weak	Medium	Good	Strong	Vivid
	Very Light	1	2	3
	Light	2	4	6	8
	Medium	2	5	7	9	10
	Dark	2	4	6	8
	Very Dark	1	2	3

As you can see in the above tables, it is a very rare gemstone that has ideal saturation and tone. That gemstone could be worth a lot of money!

Gem Grading