How to evaluate colored gemstones:
Though most people think only diamonds are graded, the evaluation of colored gems is far more complicated, and, if you wish, a life-time of learning, a never-ending journey of discovery with surprises tempting from every gem variety. A famous gemmologist once remarked that "You may learn all there is to know about white diamonds in an afternoon, but study opals for years and know half ...", or thereabouts.
Scary? Sure is!
There are two short-cuts for the new-comer or the occasional buyer. Both should be considered equally, but in their own way:
1. Indispensable, even for a professional, are third-party lab-reports. They are considered the 'scientific truth', although heated discussions about the results from different laboratories are no rarity. More and more, buyers of very expensive gems have several reports made for the same gem and compare results. Some believe only in one lab, others swear by a different one. Thus, even scientific truth can become difficult in colored gems. Books could be filled with opinions and anecdotes on the topic, but you need not worry about these details. In most cases and for the main issues, professional laboratories, small or giant, deliver all base facts; as do many lesser known local labs but for these you need trust in the sellers' opinion and his/her regard for the local laboratory. Some small labs are run by very experienced gemmologists, even famous specialists, who may well be far more dedicated to 'scientific truth' than an employee in one of the global super labs. Ask for an opinion when needed.
2. Leading right to the 2nd short-cut for every gem buyer. Because scientific truths are such rare animals, most big websites offer their own, broader reports about a gems' quality. These reports are but opinions, the owner's judgement based on his/her study of the gemstone. It is considered dishonest to dress up home-made grading as independent laboratory reports, and most professional traders make clear what is their own opinion and what is a lab's testing result. The same should be true for so-called appraisals, imagined market values set by the seller (not the market).
We use a standardized grading system to describe our gems within comparable parameters. Developed over fifteen years, it varies only if the gem-type demands additional information (for example the quality of stars or the strength of a color-change).
Here are three basic rules the trade has agreed upon (this happens):
- All grading is done under a maximum ten-fold lens. What cannot be seen under such a lens 'does not exist' for grading purposes.
- Most varieties and features are judged from the front, the main visible part, or the so called 'face-up' that would be most important after a setting in jewelry. Inclusions, for example, that are visible only from the backside may be mentioned in a grading report but are not relevant for its clarity, as long as the inclusion is invisible from the front and under a ten-fold lens.
- Few exceptions aside, gemstone grading, especially color judgement, is done under full natural in-doors daylight. Photos should be produced under the same conditions. Wherever this is not possible, say July in the Antarctica or in a nuclear bomb shelter, artificial daylight is the only alternative.
Read also about the right lens and the right light.
Cornflower or Centaurea:
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A gem's value is primarily based on its color. Here are the basics you need:
What is a color?
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.
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What is saturation?
Saturation is the amount of gray in color. A fully saturated color, 100%, would not contain any gray at all. Or, put differently, pure gray is no color but black, or no gray in the absence of color is white (which in the form of light is the sum of all colors but then it gets philosophic).
Yet, nature rarely does 'perfection'. No 100% saturation in any gem, but always a little bit of gray to deal with. As a rule, the higher the saturation (less gray) the more expensive the gem (with the usual exceptions).
What is a hue?
Hue is the color perceived by a subjective observer, usually a combination of primary and secondary hues. BUT white, black and gray are no colors, they have no hue.
Some hues in the main gem-varieties, like red, pink and blue in corundum, are (today) considered more valuable than others (e.g. yellow or purple). This has and continues to change with fashion, over time and between cultures. Purple for example once was the most expensive color in Europe, a royal privilege.
What is a tint?
A dash of color mixed into another is called a tint. A tint is lighter and less saturated than a 'real' color. All color will have a tint of gray but, remember, gray is not a color. A tint of violet in red makes for an especially valuable ruby.
Generally, less tint means a purer color and a higher price with the usual exception waiting to confuse; such as the tint of violet that makes for especially valuable ruby.
How to describe a color?
You may describe a stone correctly as "blue (hue) mixed with 20% gray (saturation) plus a tint of yellow with little white (tone)".
Such descriptions are hard to imagine and not very marketing friendly, as are scientific codes in multi-dimensional color-spaces like Hex#AFD645 (68.6% red, 83.9% green and 27.1% blue).
All unattractive, difficult to communicate.
Color-professionals therefore use more illustrative descriptions such as "ivy green", "cornflower blue" or "salmon orange" in connection with attributes like "strong" or "vivid". Global consumer products like Windex-Blue, Coca-Cola Red or Bubble-gum pink are equally helpful.
What is a color grade?
Color-grade describes the quality of the dominant color in a gemstone.
Some varieties (e.g. the Padaparadscha), which are defined by a combination of dominant colors (e.g. pink and orange) will receive a high color grade not from the purity of the main color but the ideal combination of two dominant colors under the absence of any other colors e.g. brown or yellow.
But grade is nothing without tone:
What is a color tone?
Colors can only be judged in combination with their tone.
Tones vary from "very light" to "very dark". Simply put, tone is the amount of black, gray or white in a gemstone.
In the extremes, a gemstone with a certain color can be almost white (light 5) or near black (dark 95) with just a hint of the main color visible. If the tone is zero, or one hunderd, NO color is present at all, the gem is white or completly black.
Only grade and tone together can describe color-quality sufficiently:
A gemstone might, for example, show a pure blue, free of green or violet, but it might be in a very light tone thus the blue is less strong (like washed-out jeans). Or it might, in the opposite, be of such a dark tone, that it appears rather black than blue (navy blue).
Gemstones with high color-grades in medium to medium-dark tones fetch the highest prices in most varieties. Exceptions are, of course, abbundant, as always in gemology.
Grade and tone are framed by color zoning, clarity, brilliancy and depth:
Untreated 2.7 carat sapphire:
"Visible" color zoning but "Free of Inclusions"
What is color zoning?
Some stones show colors only in certain 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: Changes in color-saturation do not stand out at first sight.
3. Gradual: Colors change visible throughout the gem but not abruptly.
4. Visible: Stone has clear color patches or layers, even hard lines.
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.
What is clarity?
The clarity of a stone is described between an ideal "Free of Inclusions" over "Lightly", "Moderately", to a worst "Heavily Included".
- Free of inclusions: Under 10x magnification no inclusions become visible.
- Very Lightly Included: A pro with a lens and good eyes might find an discreet inclusion, a colorless bubble or a needle but nothing ugly.
- Lightly Included: Inclusions become visible under a 10x magnification but not (or rarely) with the unaided eye.
- Moderately Included: One might see inclusions with the naked eye, but they should not dominate the stone
- Heavily Included: Inclusions are clearly visible and influence the stone's appearance and may not be durable enough for jewelry.
Clarity-judgements are done in the front-view only. An inclusion that is visible from the back or the side only does NOT count even if we may comment on it in the grading report.
|4.24 ct Sapphire|
Photo above: "Heavily Included" sapphires with "Visible" color zoning.
Remark on photo: While the yellow is too unevenly included it is not unattractive, though its value will be somewhere around only 5-10% of a similarly colored stone which is "Free of Inclusions".
What is brilliancy?
With '% brilliancy' we describe the estimated maximum of light which a stone 'throws' back at you under good light condition. High brilliancy is, amongst others, the result of skilled cutting, clarity and given values like dispersion or the RI (Reflective Index) of a variety.
The given number, say 66%, represents a subjective judgement of the person grading. It's not rocket-science but simply an estimate that a maximum two-third, 66%, of the gem glitters under good light conditions. It may well be 70% or 65% for a different set of eyes but precision is not the purpose of this value. What you do get, is a basic pointer to the amount of brilliancy you can expect from a gem. If the value is 25% or less you are probably looking at what may be called a 'color-gem' like many emeralds or silky sapphires, which charm with a vivid color but not glitter. If the report says 95% you can well expect a fountain of sparkle.
What is depth?
Depth is the height of a stone divided by its width. The "ideal" range lies between 60% and 80%. It is mainly determined by the given shape of the rough stone and the lapidary's ability to optimize weight-loss against shape and brilliancy. Under 50% a stone might be called shallow and will most likely be 'windowed'. A shallow 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 easily.
What is cutting grade?
Our "Cutting Grade" summarizes the overall quality of the lapidary's work, his general choice of design, the main table's orientation to optimize the face-up color, precise facet meeting points, the gems' final polish and a book load of topics only a pro needs to understand (that's our job). Modern, mostly CAD-based faceting is called 'precision-cutting' and usually deserve an 'Excellent' as grade, as do daring works of art or special effects using for example color-zoning or multi-colored rough to their advantage. Here, or with a marker to the comment, would we mention any flaws or weaknesses in the cut, like the most dreaded window (a rarity here), a chip or an asymmetric back.
What is "overall grade"?
If you want to keep things real simple you just have to look at the overall grade which is described by five levels:
- Excellent: Far above average and flawless. This quality is not available in ready-made jewelry and is mostly acquired by long-term investors for heirloom collections or special occasion jewelry designed around the gem. An additional '+' or a very rare double '++' are reserved for perfect gems without any flaws what-so-ever, perfect color, cut and crystal combined with extreme natural rarity in size, shape, clarity and color (e.g. a well sized unheated Burma ruby, plus a 'free of inclusions' and precision cut, a clean un-oiled vivid emerald or untreated round neon pink sapphire or similar quality padparadschas).
- Very Good: Above average in all criteria with one or two minor flaws. Our 3*NOS of excellence - no treatment, no window, no inclusions - are always fulfilled.
- Good: Average quality with strengths and weaknesses. One of our 3*NOS may be under discussion but not utterly compromised in a disturbing or ugly form.
- Fair: Average quality with one or two obvious flaws. Usually not in our inventory, except when some other quality stands out.
- Poor: Major imperfections. Represents at least 75% of the commercial market.
From our own mining operations, we can attest that 900 out of 1000 gems coming from an average Sri Lankan mine will fall into the category "poor" and "fair", with while only one(!) might receive an "excellent".
BUT: Whatever gemologists, traders, miners, jewelers or grading reports say, you are the only one authorized to judge beauty.
The less you like what everybody else does, the better for your budget.
Here are some guidelines to prices ($/carat) for manually mined, individually cut, certified and untreated Ceylon gemstones based on the overall grade as we define it.
Whatever somebody tells you, there is no fixed market price for colored gems (for white diamonds, yes, and falling daily) but the price of any unique colored gem including colored diamonds is the one that a buyer and a seller agree upon at a certain time.
Nothing else counts.
3. Gemstone sizes:
Read here to judge sizes for jewelry.
4. Gems and Photos:
Today there are more good gem-photos than good gems in the market.
Read an in-depth study here: Gemstones on Photo
We do not color enhance or brighten or darken our photos. Our photos are made with a "normal" Nikon 5400 and every stone is shot individually. We never re-use old photos.
Left untouched, photos might show inclusions to strongly, weaken or strengthen its color, make a light stone darker or vice versa. If that is so, we mention it in our comment at the end of the grading report.
If you think a photo differs from our grading, you can assume that the grading is closer to reality than the photo. In any case our stones convince best in person.
Our hand-shots: Please take note that our hand photos are made with fingers of US-ring-size TWELVE (no hand-model within our budget). Thus, if you have a ring-size of, say, SIX the gem will look twice as large on your fingers.
Here is a very different approach which may help to understand the complexity of this market. Let's imagine you are saving money by accepting flaws.
Most aspiring gem-lovers are overwhelmed by the depth and width of the market. If they have been confused in a B&M jeweler, a quick web-search is going to do the rest. But, alas, there is no competence for the lazy. Selecting antiques, real estate or vintage cars requires homework too.
101 buying guides offer good reading and places like this help. Be prepared to spend weeks in a fog but do not despair. Collecting gems is a passion and the learning never ends.
Here is a fresh perspective for the determined beginner. It comes out of a thousand discussions with early stage buyers and their consecutive decisions.
First allow this axiom: "No natural gem is perfect."
The deeper your knowledge the better your choices will get, but there is no final word. All veterans know this.
Consider that 95% of what comes out of a mine goes straight back into the pit. Most rough material is too small, too included, too dull or too unshapely to be cut into gemstones.
Only the remaining 5% make it into sales and they all are flawed.
It is those flaws that need attention: Evaluating gemstones means recognizing imperfection.
Here is an exemplary list of common flaws rated with negative numbers:
1. Clarity: From lens-only bubbles (-1) to visible black inclusions (-3)
2. Windows: From small and symmetric (-2) to big and uneven (-5)
3. Color-zoning: From faint (-1) to dramatic (-2)
4. Cutting: From not-precise (-2) to native egg-shape (-5)
5. Treatment: From heat-only (-1) to surface coating (-10)
6. Color: From off-ideal (-1) to pale or dark (-5)
1) A terrible gem could here, theoretically, make it to minus 30. Yuk!
2) Color includes tone and hue
This individual list has no fixed reference. You can add or disregard issues or give reverse ratings. It needs to look different for cat's eyes, pairs or color changers; in fact, the list will look different for every single purchase.
Professionals make this kind of evaluation automatically and in seconds.
You need not to be that fast. Also, you need not think of anything other than what you want or like; and that is entirely up to you. You may find a specific color perfect and some treatment acceptable while other buyers might not be interested in the same stone for half the price.
As always, if you want what everybody wants you need to dig deeper.
The one perfect stone would have no window (not even a tilt window), be free of inclusions but not synthetic, have no color-zoning, sport an art-full precision-cut, be untreated and have exactly the hue you want it in and in exactly the right tone. Plus, it needs be in the desired size and shape with ideal proportions, be of your preferred origin and have a perfect certificate. Finally, it must be for sale within your budget.
A tall order!
In reality, we have to allow for some negotiable flaws, define restrictions in budget and time.
Practically, you might be shopping for a round yellow sapphire in 2 carats and you need to order soon. The web shows legitimate offers between 250 and 2000.
Study the flaws that make the difference between 250 and 2000.
A terrible window may bring you from 2000 to 1000, a pale hue downs it to 500 and heat may bring you to 250.
Below 250 (e.g. bad window, pale, BE-treated and included) the definition of gem-quality sapphire gets shaky.
If you like numbers you may actually chart your alternatives with prices and flaws on a rough scale.
More confused? In the end, follow your heart, not the numbers and remember:
"There may always be a better one".