In our last article, ‘Padparadscha Sapphire – Understanding Color Grading’, we discussed how gemologists use the GIA Color Stone Grading System when judging gemstones. Gemology is a vastly interesting field of endeavor, and gemologist ‘wannabes’(like me for example)will find that learning all one can about gemology including grading gems is a fun and rewarding pastime. Please refer to our article introducing 'Our Gemology Expert' Barbara Smigel, for references to her fabulous online Introduction to Gemology Course for all of you who may be interested in this fascinating subject.
The three key charts in the GIA Type Colored Stone Grading System, are GIA Type Color Scale, GIA Type Tone Scale, and GIA Type Saturation Scale are provided below for your reference...
Have fun and good luck in finding the perfect gemstone!
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Color Scale
Hue is described as the shade, tint or sensation of a color. The GIA has 31 Hues and the he complete GIA GemSet® has 324 sample hue colors with varying Tones and Saturations. In addition we put RGB (Red Green Blue) and HEX codes for your reference.
Key Code Name HEX RGB
R red FA0303 R:250 G:3 B:3
oR orangy red EE2102 R:238 G:33 B:2
RO/OR red-orange or orange-red FB3E00 R:251 G:62 B:0
rO reddish orange FE6000 R:254 G:96 B:0
O orange F87B00 R:254 G:96 B:0
yO yellowish orange F6A400 R:246 G:164 B:0
oY orangy yellow F7CD00 R:247 G:205 B:0
Y yellow F8F800 R:248 G:248 B:0
gY greenish yellow CEE600 R:206 G:230 B:0
YG/GY yellow-green or green-yellow B0DD00 R:176 G:221 B:0
styG strongly yellowish green 7BCE00 R:123 G:206 B:0
yG yellowish green 4DC100 R:77 G:193 B:0
slyG slightly yellowish green 26C200 R:38 G:194 B:0
G green 00C000 R:0 G:192 B:0
vslbG very slightly bluish green 00BE26 R:0 G:190 B:38
bG bluish green 00BA4A R:0 G:186 B:74
vstbG very strongly bluish green 00B96F R:0 G:185 B:111
GB/BG green-blue or blue-green 00B893 R:0 G:184 B:147
vstgB very strongly greenish blue 09B4B4 R:9 G:180 B:180
vslgB very slightly greenish blue 0A59AA R:10 G:89 B:170
B blue 0916A5 R:9 G:22 B:165
vB violetish blue 0808A0 R:8 G:8 B:160
bV bluish violet 7B0AB4 R:62 G:8 B:170
V violet 7B0AB4 R:123 G:10 B:180
bP bluish purple C70BC7 R:199 G:11 B:199
P purple D40CB1 R:212 G:12 B:177
rP reddish purple E90A9E R:233 G:10 B:158
RP/PR red-purple or purple-red F50E80 R:245 G:14 B:128
stpR strongly purplish red F80E5C R:248 G:14 B:92
slpR slightly purplish red F20E33 R:242 G:14 B:51
R red FA0303 R:250 G:3 B:3
Pk pink (exception) FFDFDF R:255 G:223 B:223
Brn brown (exception) B7770D R:183 G:119 B:13
Tone
Tone is described as the relative lightness or darkness of a Hue. The GIA Tone Scale is divided into 11 grades, 0 to 10, with 0 being colorless to 10 being black.
Key Scale Code Name HEX RGB
0 c Colorless or White FFFFFF R:255 G:255 B:255
1 ex1 Extremely light F8F8F8 R:248 G:248 B:248
2 v1 Very light F0F0F0 R:240 G:240 B:240
3 l Light E8E8E8 R:232 G:232 B:232
4 ml Medium light D6D6D6 R:214 G:214 B:214
5 m Medium C5C5C5 R:197 G:197 B:197
6 md Medium dark A3A3A3 R:163 G:163 B:163
7 d Dark 888888 R:136 G:136 B:136
8 vd Very dark 646464 R:100 G:100 B:100
9 exd Extremely dark 424242 R:66 G:66 B:66
10 bl Black 000000 R:0 G:0 B:0
Saturation
Saturation is described as the strength or purity of a Hue. The GIA Saturation Scale is from 1 to 6. The lower numbers such as 1, 2 or 3 of warm colors such as red, orange or yellow and tend to look brownish and the cool colors such as blue and green tend to look grayish. Level 4 no longer shows either grayishness or brownishness, while neither is strong or weak. Level 5 is strong and level 6 being vivid, almost over colored.
Scale Code Name
1 gr(br) grayish (brownish)
2 slgr slightly grayish(brownish
3 vslgr very slightly grayish(brownish)
4 mst moderately strong
5 st strong
6 v vivid
