Grading
Grading of our gemstones
The descriptions of our gemstones include:
Colour
Clarity
Weight
Dimensions
Cut
Treatments
Describing the colour of a gemstone is very difficult and may be quite ambiguous. Photographing a gemstone is a challenge too and the pictures often don't reflect every aspect of the stone correctly. Additionally, the viewer's computer monitor may make the image look differently than if it was displayed on a different screen.
The GIA colour grading system provides a tool for describing the colour of a coloured gemstone. The colour is generally assessed from above through the table in standard daylight.
The GIA colour grading system breaks the colour of a gemstone in three components: hue, tone and saturation. The CIA colour code consists of abbreviations and numbers representing these three characteristics.
Example: stpR 3/4 stands for 'strongly purplish red' with a light tone and a moderately strong saturation. This colour could be addressed as light clean pink.
The colour grading specified with our products are indicative only. We are not liable for dissenting opinions regarding the choice of colour, tone or saturation classes.
The following tables list the codes and scales used in the GIA colour grading system.
Hue
| Code | Name |
|---|---|
| R | red |
| oR | orangey red |
| RO/OR | red-orange or orange-red |
| rO | reddish orange |
| O | orange |
| yO | yellowish orange |
| oY | orangey yellow |
| Y | yellow |
| gY | greenish yellow |
| YG/GY | yellow-green or green-yellow |
| styG | strongly yellowish green |
| yG | yellowish green |
| slyG | slightly yellowish green |
| G | green |
| vslbG | very slightly bluish green |
| bG | bluish green |
| vstbG | very strongly bluish |
| GB/BG | green-blue or blue-green |
| vstgB | very strongly greenish blue |
| vslgB | very slightly greenish blue |
| B | blue |
| vB | violetish blue |
| bV | bluish violet |
| V | violet |
| vP | violetish purple |
| P | purple |
| rP | reddish purple |
| RP/PR | red-purple or purple-red |
| stpR | strongly purplish red |
| slpR | slightly purplish red |
Tone
| Scale | Name |
|---|---|
| 0 | colourless or white |
| 1 | extremely light |
| 2 | very light |
| 3 | light |
| 4 | medium light |
| 5 | medium |
| 6 | medium dark |
| 7 | dark |
| 8 | very dark |
| 9 | extremely dark |
| 10 | black |
Saturation
| Scale |
Name |
| 1 | greyish (brownish) |
| 2 | slightly greyish (brownish) |
| 3 | very slightly greyish (brownish) |
| 4 | moderately strong |
| 5 | strong |
| 6 | vivid |
The clarity of a gemstone is assessed with a hand lens with a 10x magnification and assigned to one of the following four groups
IF (internally flawless): internally flawless under 10x magnification
VS (very slightly included): very small inclusions or fissures visible under 10x magnification
SI (slightly included): small inclusions or fissures visible to the naked eye
I (included): inclusions or fissures prominently visible to the naked eye
Our scales are precise to 0.0001g (0.0005ct) and are regularly cross checked with certified scales in a accredited laboratory. Weight indications for cut gemstones are rounded to 0.01ct.
Measurements of length, width and depth are performed with callipers with a precision of 0.01mm.
We classify our faceted gemstones assessing proportions, symmetry and polishing as well as the brilliance of a stone and negative features like windows or extinction. Our cut classification is threefold:
native: several factors may be non-ideal.
commercial: generally good cutting quality; polishing, proportions, symmetry or other parameters may be slightly off the optimum
precision: the cut is perfect in every respect: perfect proportion and symmetry and excellent polishing.
Our gemstones are generally untreated and natural, i.e. our stones did not experience any heating to enhance colour, or oiling for clarity enhancement or other treatments. We can guarantee for this as we are in control of the whole production chain from extraction of the mine to the faceting process. In the exceptional case where stones were treated (e.g. oiling of emeralds) it is clearly stated in the description of the individual stone.
In mines where the solid pegmatite is being mined, fire setting may be allpied to loosen the rock. This leads to a heating of the rock and may induce a change in colour of aquamarine. However, since the stones are still in the ground at that point, we do not speak of (an intended) treatment or enhancement.
Since most gem rough is presented in a bag with baby oil to allow the assessment of clarity in the bush, some rare cases may occur where some of this baby oil remains in deep fissures within the faceted stones, which resembles slight clarity enhancement.