When buying Coloured Gemstones, it is important to consider the following:-
There are "3" factors that determine quality.
Colour can be described in terms of:
The human eye can discern 150 different hues. Basic hue names are: Red, Orange, Yellow, Green, Blue, Violet and Purple.
Modifying names are then used to describe hues that fall in between these terms, such as: Bluish, Greenish, Orangy plus other modifiers such as: Slightly, Strongly.
Tone is described using the G.I.A Tonal scale ranging from 0 (Colourless) to 10 (Black).
Saturation is assessed on a scale ranging from 0 (Neutral) to 6 (Vivid).
In warm colours (i.e Red, Orange, Yellow), lower levels of saturation will appear brownish.
In cool colours (i.e Green, Blue, Violet or Purple), lower levels of saturation will appear grayish.
In some cases, when dealing with stones of lower saturation, the use of such modifiers as brownish or pinkish may be used.
Should be checked first with the naked eye, then with 10X magnification noting any obvious inclusions or blemishes.
Gemstones are divided into 3 clarity types:
Five factors to consider when "Clarity Grading" :
Beryl | Topaz | Chrysoberyl |
---|---|---|
Aquamarine | Blue | Green |
Green | Yellow | Yellow |
Morganite (Pink Beryl) | Orange | |
Yellow Beryl | Pink | |
Red | ||
Quartz | Spodumene | Tourmaline |
Smoky | Kunzite | Green |
Green | ||
Zircon | Zoisite | |
Blue | Tanzanite |
Andalusite | Topaz |
---|---|
Alexandrite (Chrysoberyl) | Blue, Orange, Yellow Parti-coloured (except watermelon) |
All Corundum | |
All Garnets | |
Iolite | All Spinels |
Quartz | Zircon |
Citrine, Amethyst, Ametrine | Green, Orange, Red & Yellow. |
Emerald | Red or Pink Tourmaline or Watermelon Tourmaline |
---|
Includes the proportions and finish of a gemstone.
May also refer to the shape or design in which the stone is cut.
The more expensive the rough, the less likely it is to be well cut due to weight retention.
Considers:
Consider:
Evaluation of the skill and care used in the fashioning process and the gems overall surface condition.
Three Steps
Rectangular 1.50 - 1.75 1.33 - 1.50 1.75 - 2.00
Marquise 1.75 - 2.25 1.66 - 1.75 2.25 - 2.50
Oval 1.33 - 1.66 1.30 - 1.33 1.66 - 1.75
Pear 1.50 - 1.75 1.30 - 1.50 1.75 - 2.00
Heart 1.00 1.00 - 1.25
Appeal : The pleasing quality of the stones face-up outline.
Examples : Misshapen lobes on a Heart Shape.
Undefined point on a Pear Shape.
Flat head and high shoulders on a pear shape.
BRILLIANCE : Light return caused by internal and external reflections.
Two Factors that diminish brilliance:
Most stones return 65 to 90% of the light.
Dark stones and ones with extreme proportion variances may result in light return below 30%.