Gemstone Review – Grading of Gemstones – ruby gemstone meaning
ruby gemstone meaning –
In the previous article I have a small intro about gemstone graduations and now here you will be able to know the completed details about the same.
Most of the people think that only diamonds have grading but there is also a set of criteria to determine the grade of the gemstones.
We have evaluated and summarized the following for grading:
A gem's value is primarily based on its color. Here are the basics you need:
Color of gems
There are three primary colors (red, blue, yellow) and three secondary colors, which are the result of mixing primary colors (purple, orange, green).
Nature often displays tertiary colors, such as red-orange, yellow-green, or blue-violet, which are a primary color mixed with a secondary color.
When a color is mixed with gray, white, or black, we need the (overlapping) definitions of saturation, hue and tints.
Saturation expresses the attribute of perception of gray of the same lightness. All grays have zero saturation. Theoretically a 100% saturation means there is 0% gray in a color.
Hue is color received to be red, purple, yellow, green etc., meaning white, black and gray have no hue.
A color mixed with white is a tint. A tint is lighter and less saturated than a color without the addition of the white.
Color Grade and Tone
Color grade describes the strength of the main color compared to other colors visible in the stone.
A 100% color grade in blue for example would imply that there are no other colors (like purple or violet) visible in the stone.
Very Good: 3-4
The color grade is simply based upon the purity of primary color. For example, the gerner the emerald, the redder the ruby, or the bluer the sapphire, the lower the numerical grade on an AGL scale. The reason the 3.04 sapphire is a 3.5 in this sample is the fact the stone has 65% blue as its primary color. It is that simple. The less primary color, the higher the numerical color grade. For example, a 60% primary color would probably be graded a 4 color.
The color scan will generally break down into three received colors that total 100%. In the sample, the sapphire is 65% blue, 20% violet and 15% green.
If there was also no gray in the stone, we would have a 100% saturation with a 100% color grade, but such a stone has never been found.
Generally the rule applies: the purer the color the higher the grade. But grade is nothing without tone:
Any color grade has to be seen in combination with tone.
In the extremes a colored stone could be white (light 5) or black (dark 95) with just a hint of color.
Very Light: 0-20
Very Dark: 90-100
Basically, tone describes the lightness or darkness of a gemstone. Color considered alone without taking into account the tone will lead to errors in interpretation. If a stone is too light in tone, the color will not be rich enough. Conversely, if a stone is too dark, it will sacrifice transparency and brilliancy.
Only grade and tone together describe color value adequately:
A stone might, for example, show a rather pure blue, free of green or violet, but it might be of a very light tone that the blue is less strong. Or it might, in the opposite, be of such a dark tone, that it appears rather black than than blue.
Gemstones with high color grades and light-medium to medium-dark tones fetch the highest prices.
Grade and tone are framed by color zoning, clarity, brilliancy and depth:
Some stones show colors only in parts or layers. To describe the strength of this common but generally unwanted effect, we use four levels:
1. None : The color is equally distributed
2. Faint : One might see changes in color saturation
3. Gradual : The color weakens in some parts but not abruptly.
4. Visible : Stone has clear color patches or layers.
Other than clarity, which is judged with a 10x lens, color-zoning is described only as far as it is visible to the unaided eye.
Free of Inclusions: FI
Lightly Included: LI1-LI2
Moderately Included: MI1-MI2
Highly Included: HI1-HI2
Excessively Included: E1-E2-E3
The clarity of a stone is commonly described as being "Free of Inclusions" over "Lightly," "Moderately," "Heavily" to "Excessively Included."
Here is how we describe a stones clarity:
– Free of inclusions : Even under 10x magnification no inclusions become visible
– Very Lightly Included: Only a pro with a lens might find an inclusion, but maybe not.
– Lightly Included: Inclusions are visible under a 10x magnification but rarely with the unaided eye
– Moderately Included : One might see see inclusions with the naked eye, but they should not dominate the stone
– Heavily Included : Inclusions are clearly visible and influencing the stone's appearance
– Excessively Included: A stone might not be durable.
It is the height of a stone divided by its minimum width. The "ideal" range lies between 60% and 80%. It is mainly determined by the given shape of the rough stone. Under 50% a stone might be called shallow. A shine stone with a light tone will find it difficult to maintain saturation. A stone with 90% depth and a dark tone on the other hand might blackout.
Brilliancy is the amount of flash the gem returns to your eyes. Most diamonds are 100% brilliant. Brilliancy in the sample is 70%. An average brilliancy of 50% means half of the stone returns flash.
Brilliancy and depth are joined in the "Cutting Grade" which also includes the general quality and precision of the lapidary's work and the finish of the stone.
Very Good: 3-4
The cutting of a gemstone numerically describes the proportions and geometry of a gem. The finish grade counts to the polish of a gem. In the sample the cutting grade is Good (5) and the finish is Very Good to Good (4-5). Unlike diamonds which are cut according to strict mathematical parameters, most colored gemstones are cut for weight retention.
- Carat Weight: 1 carat or larger
- Color: Good (6) or better
- Tone: Ideal tone for ruby, sapphire and emerald ranges from medium to dark (65-85). Ideal tone for other gem types varies from light to medium (20-65).
- Clarity: Moderately Included Two (MI2) or better
- Average Brilliancy: 50% or more
- Cutting / Finish: Good (6) or better
Laboratories for Gemstones Grading
There are a number of laboratories which grade and provide reports on gemstones.
– International Gemological Institute (IGI), independent laboratory for grading and evaluation of diamonds, jewelery and colored stones.
– Gemological Institute of America (GIA), the main provider of education services and diamond grading reports.
– Hoge Raad voor Diamant (HRD Antwerp), The Diamond High Council, Belgium is one of Europe's oldest laboratories.
– American Gemological Society (AGS) is not as widely recognized nor as old as the GIA.
– American Gem Trade Laboratory which is part of the American Gem Trade Association (AGTA), a trade organization of jewelers and dealers of colored stones.
– American Gemological Laboratories (AGL)
– European Gemological Laboratory (EGL)
– Gemmological Association of All Japan (GAAJ-ZENHOKYO), Zenhokyo, Japan, active in gemological research.
– Gemmological Institute of Thailand (GIT) is closely related to Chulalongkorn University
– Gemmology Institute of Southern Africa, Africa's premium gem laboratory.
– Asian Institute of Gemological Sciences (AIGS), the oldest gemological institute in South East Asia, involved in gemological education and gem testing.
– Swiss Gemmological Institute (SSEF), focusing on colored gemstones and the identification of natural pearls.
– Gübelin Gem Lab, the traditional Swiss lab.
– Grading of Gemstones
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