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| When buying Coloured Gemstones, it is important to consider the following:- |
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Is the stone Natural or Synthetic? |
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Is the colour natural? |
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Are there any noticeable inclusions? |
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Do they affect the durability of the stone? |
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How well is the gemstone proportioned? |
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If the gemstone possesses "Optical Phenomena", is it well defined? |
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What is the weight of the gemstone? |
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How do I care for the gemstone? |
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| Evaluating Coloured Gemstones |
| There are "3" factors that determine quality. |
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| Colour |
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The most important factor in the evaluation of Coloured Gemstones. |
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The gemstone should be checked under normal daylight, fluorescent light and incandescent lighting noting any colour change. |
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| Colour can be described in terms of: |
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Hue: This is the dominant and secondary colour visible in a stone. |
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Tone: This is the sensation of the depth or darkness of the colour perceived by the eye. |
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Saturation: This is the strength, purity, intensity of the hue present. |
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| Hue |
| The human eye can discern 150 different hues. Basic hue names are: Red, Orange, Yellow, Green, Blue, Violet and Purple. |
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| Tone |
| Tone is described using the G.I.A Tonal scale ranging from 0 (Colourless) to 10 (Black). |
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| Saturation |
| 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. |
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| Colour Grading Overview |
| Thoroughly clean the stone. Hold the stone by the girdle in the tweezers. Look at the stone face-up from about 18" away in strong, diffused, daylight equivalent lighting (with the light 6 to 10 inches above the stone) Estimate the hue of the dominant and secondary colours. Estimate the tone. Estimate the saturation. |
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| Clarity |
| Gemstone 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: |
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Type 1: Gemstones that are expected to form without inclusions (i.e. Aquamarine). Even minor inclusions will detract from their desirability. |
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Type II: Form with moderate inclusions (i.e. Ruby and Sapphire). |
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Type III : Always found with inclusions (i.e. Emerald) |
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| Five factors to consider when "Clarity Grading”: |
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Nature of the inclusion. (v) Position. |
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Size. |
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Colour and Relief. |
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Number |
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| Clarity Classifications |
| TYPE I |
| Beryl |
Topaz |
Chrysoberyl |
| Aquamarine |
Blue |
Green |
| Green Beryl |
Yellow |
Yellow |
| Morganite (Pink Beryl) |
Orange |
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| Yellow Beryl |
Pink |
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Red |
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| Quartz |
Spodumene |
Tourmaline |
| Smoky |
Kunzite |
Green |
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Green |
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| Zircon |
Zoisite |
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| Blue |
Tanzanite |
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| TYPE II |
| Andalusite |
Tourmaline |
| Alexandrite (Chrysoberyl) |
Blue, Orange, Yellow Parti-coloured (except watermelon) |
| All Corundum |
| All Garnets |
| Iolite |
All Spinels |
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| Quartz |
Zircon |
| Citrine, Amethyst, Ametrine |
Green, Orange, Red & Yellow. |
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| TYPE III |
| Emerald |
Red or Pink Tourmaline or Watermelon Tourmaline |
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Clean the stone. |
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Hold the stone by the girdle in tweezers or stone holder. |
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Look at the stone with the naked eye in the face-up position. |
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Turn the stone to view from all angles. Look at the stone under 10X with dark field illumination. |
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Turn the stone to view from all angles. |
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Use overhead light to check for surface blemishes. |
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Assign a clarity grade. |
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| Cut |
| Cut 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. |
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| Proportion Grading |
| Considers: |
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Beauty |
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Appeal |
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Practicality of outline and dimensions (including the ease in which the stone can be mounted and the presence of excess weight that does not contribute to beauty). |
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| Finish Grading |
| Consider: |
| Evaluation of the skill and care used in the fashioning process and the gems overall surface condition. |
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| Proportions |
| Three Steps |
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Face-up Outline |
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Brilliance |
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Profile |
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| Face-Up Outline |
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Balance: The equality between corresponding parts of the stone in the face-up position. |
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Length to Width Ratio: The relationship between the length and the width of a stone. |
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| Shape Preferred Acceptable |
| 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 - 1.25 |
| 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. |
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| Two Factors that diminish brilliance: |
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Windowing: A washed out area generally seen through the table caused by "light leakage". |
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Extinction: Areas of darkness visible through the crown. |
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| Most stones return 65 to 90% of the light. |
| Dark stones and ones with extreme proportion variances may result in light return below 30%. |
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| Profile |
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Table size : 55 to 65% |
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Girdle Thickness: Should be of medium thickness, thicker towards the points to prevent breakage. |
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Total Depth : 60 to 75% |
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Crown Height / Pavilion Depth Ratio : 1 : 3 (25% crown to 75% pavilion) or 1 : 2 (33% crown to67% pavilion) |
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Bulge Factor: Minimal bulge is acceptable in Step-Cuts due to the slight changes in angle necessary from one row of facets to the next. |
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Balance or Symmetry: The equality between the corresponding parts when viewed from the side or the end. |
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| Finish |
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Polish: Surface characteristics not included under "Clarity". As a result of the polishing process or wear. |
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Symmetry: consistency of the shape, positioning and arrangement of facets and the balance of the overall facet design. |
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| Gem Store |
| The following types of Gemstones in the table below are readily available at Real Stone Gem store. However Gemstones of other configurations as per requirements can be delivered on order. |
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| To place your orders send email to contact@realstone.in |
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