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Grading

Grading of our gemstones

The descriptions of our gemstones include:

Colour
Clarity
Weight
Dimensions
Cut
Treatments

 

Colour grading

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

ScaleName
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

 

Clarity grading

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

 

Weight

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.

 

Dimensions

Measurements of length, width and depth are performed with callipers with a precision of 0.01mm.

 

Cut grading

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.

 

Treatments

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.

 


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