Evaluating Gemstones

Evaluating
Gemstones

Grading Gemstones -- a Brief Introduction

The Gemological Institute of America (GIA) terms by which Topazery gemstones are graded are briefly explained on this page. Like diamonds, gemstones are graded by color, cut, clarity and carat weight. When grading a gemstone, a gemologist measures a gemstone's weight in carats, and the gemstone's dimensions [length, width, and depth] in millimeters. Clarity and color are also evaluated. Color in gemstones is composed of three different qualities: hue, tone, and saturation.

Clarity Categories for Gemstones

Clarity is a gemstone's relative freedom from clarity characteristics. The clarity grade is based on how visible inclusions are and how they affect the gemstone's beauty and durability. Some gemstones tend to have more inclusions than others. For this reason, clarity ranges for gemstones are grouped into three types: Type I, Type II, and Type III. Type I stones are usually eye-clean with no inclusions visible to the naked eye. Type II stones typically show some eye-visible inclusions that don't detract from the gem's overall beauty. Type III stones are almost always included and show eye-visible inclusions.

	VVS, Eye-Clean	VS, Slightly Included	SI1-SI2, Moderately Included	I1-I2, Heavily Included	I3, Severely Included
Type I	The stone appears clean to the unaided eye.	Minute inclusions are difficult to see without a 10x loupe.	Minor inclusions are somewhat easy to see without a 10x loupe.	Inclusions are prominent.	Prominent inclusions have a severe impact on appearance, durability, or both.
Type II	The stone appears clean to the unaided eye.	Minor inclusions are somewhat easy to see with the unaided eye.	Noticeable inclusions apparent to the unaided eye.	Inclusions are prominent.	Prominent inclusions have a severe effect on appearance, durability, or both.
Type III	The stone appears clean to the unaided eye.	Noticeable inclusions apparent to the unaided eye.	Obvious inclusions very apparent to the unaided eye.	Inclusions are prominent.	Prominent inclusions have a severe impact on appearance, durability, or both.

Color in Gemstones

Color is the first thing you notice about a gemstone. Color is mainly caused by the gem's selective absorption of certain wavelengths of light. Gemologists refer to this color as the gem's body color. In gemstones, color consists of three components: hue, tone and saturation.

Hue is the first impression of a color and is what you see when you first look at a gem. The GIA gemstone grading system uses 31 hues to describe color in a gemstone.

Tone is the lightness or darkness of color and ranges from light to medium to dark. Three key standards are 3 (light), 5 (medium), and 7 (dark).

Saturation is the intensity of a gemstone's color and is measured from dull to strong to vivid. The GIA uses 6 saturation measurements.

Color Hues for Gemstones

Purple	P
reddish Purple	rP
Red-Purple or Purple-Red	RP/PR
strongly purplish Red	stpR
slightly purplish Red	slpR
Red	R
orangey Red	oR
Red-Orange or Orange-Red	RO/OR
reddish Orange	rO
Orange	O
yellowish Orange	yO
orangey Yellow	oY
Yellow	Y
greenish Yellow	gY
Yellow-Green or Green-Yellow	YG/GY
strongly yellowish Green	styG
yellowish Green	yG
slightly yellowish Green	slyG
Green	G
very slightly bluish Green	vslbG
bluish Green	bG
very strongly bluish Green	vstbG
Green-Blue or Blue-Green	GB/BG
very strongly greenish Blue	vstgB
greenish Blue	gB
very slightly greenish Blue	vslgB
Blue	B
violetish Blue	vB
bluish Violet	bV
Violet	V
violetish Purple	vP

Tones for Gemstones

2	very light
3	light
4	medium light
5	medium
6	medium dark
7	dark
8	very dark

Gemstone Saturation Scale

Warm colors	brownish	slightly brownish	very slightly brownish	moderately strong	strong	vivid
Tone	1	2	3	4	5	6
Cool colors	grayish	slightly grayish	very slightly grayish	moderately strong	strong	vivid