Some Gem Dealers Yet to Take a Shine to Proposed Rules Again
Judging Quality - The Four C's
JUDGING QUALITY
The Four C'southward
CONTENTS
Quality in colored gemstones
The appearance of a colored gem is a combination of many divide factors, each of which is related to, and affected by, the others. It is precisely the complication of these intertwined relationships that has bedeviled all attempts to quantify quality. And yet, every time a dealer buys a precious stone, a quick mental analysis is made, usually within seconds. In grading any gem, ane must be cognizant of, but not get lost in, the details. When all the minutiae has been pored over ad infinitum, take a footstep back and just expect at the jewel. In the historic period of high-powered microscopes this may plant a radical concept, but 1 which is necessary.
In the following essay, nosotros volition examine in detail the features that make upwards a fine colored gemstone.
The four C's
Determining the quality of a gemstone involves what jewelers refer to every bit the "4 C'south." They are as follows:
- Color
- Clarity
- Cut
- Carat Weight
To these, we tin also add a fifth C, Color Coverage
While these factors are well defined for diamond, no universally-accepted organization exists for colored gems.
Color
The First C
For a colored stone (whatsoever gem other than diamond), color is the near of import factor in determining quality.
To the color scientist, given an opaque, matt-finished object, in that location are three dimensions to color:
- Hue position
- Saturation (intensity)
- Tone (lightness or darkness)
For colored gemstones, there is too a fourth factor:
- Color coverage
3-dimension view of a color solid. Illustration courtesy of Minolta Us.
Hue position describes the position of a colour on a color wheel. Illustration © R.Westward. Hughes
The relationship between tone (lightness) and saturation. Illustration © R.W. Hughes
Hue position. The position of a color on a colour wheel, i.e., red, orange, yellow, green, blue and violet. Majestic is intermediate betwixt red and violet. White and blackness are totally defective in hue, and thus achromatic ('without colour'). Dark-brown is not a hue in itself, but covers a range of hues of depression saturation (and oft high darkness). Classic browns fall in the yellow to orangish hues.
Generally speaking, gems with hues that most closely resemble the ruddy, dark-green and blue (RGB) sensors in our eyes are nearly popular. Thus the colored gem trinity, ruby, emerald and sapphire. But there is much about hue that is a personal preference and volition depend upon an individual'due south personal taste.
Three greenish gems, showing a variation in hue position. The round centre stone is a straight green, while the trillion-cut stone at left is a more than yellowish green and the oval stone at right a slightly blue dark-green. Generally speaking, hue position is of less importance than saturation. Photograph: Wimon Manorotkul
Saturation (intensity). The richness of a color, or the caste to which a color varies from achromaticity (white and black are the ii achromatic colors, each totally lacking in hue).When dealing with gems of the same basic hue position (i.e., rubies, which are all basically red in hue), differences in color quality are mainly related to differences in saturation, because humans tend to be more attracted to highly saturate colors.The strong cherry-red fluorescence of most rubies (the exception beingness those from the Thai/Cambodian edge region) is an added boost to saturation, supercharging information technology past other gems that lack the effect.
4 blue sapphires showing a variation in saturation and tone. Stone 1 possesses a calorie-free tone and low saturation. Rock two is close to ideal in both tone and saturation. Stone 3 has greater saturation than Stone 2 in some areas, merely its overall tone is too night and it shows too much extinction. Stone 4 is and then dark in tone that its saturation is reduced. Note that inclusions are far more visible in stones of light tone than those of dark tones. Photo: Wimon Manorotkul
Tone. The caste of lightness or darkness of a color, equally a function of the amount of light captivated. White would have 0% darkness and blackness 100%. At their maximum saturation, some colors are naturally darker than others. For instance, a rich violet is darker than even the most highly saturated yellowish, while the highest saturations of red and green tend to be of like darkness. Annotation that every bit saturation increases, then likewise does tone (since more light is being captivated. However, in that location reaches a betoken where increases in tone may upshot in a decrease in saturation, as a color "blackens."
When judging the quality of a colored jewel, tone is an important consideration. Before buying, information technology'southward ever a good idea to consider the lighting conditions under which it volition be worn.Look for stones that wait good fifty-fifty under the low lighting conditions you find in the evening or in a restaurant, for these are typically the weather nether which fine gems are worn and viewed. Also view gems at arm's length and expect for those that are attractive fifty-fifty at a distance. Exceptional gems will look bully under all lighting conditions and viewing distances.
CLARITY
The Second C
Clarity is judged past reference to inclusions.Magnification can exist used to locate inclusions, merely with the exception of inclusions which might touch immovability, only those visible to the naked middle should influence the last grade.In this style, colored gems are very dissimilar from diamond. Indeed, in certain cases (Kashmir sapphires being a classic example), the inclusions tin can actually heighten dazzler and value.
Different levels of clarity are visible hither in these spessartine garnets from Nigeria. The oval stone at left is eye clean, i.e., with no clarity defects visible to the unaided eye. In the pear-shaped centre stone, obvious clarity defects are visible, while in the trillion-shaped stone at correct, they are even more obvious. Photos: Wimon Manorotkul
There are two cardinal factors in judging clarity. These are:
Visibility of inclusions
- Size: Smaller inclusions are less distracting, and thus, amend.
- Number: Generally, the fewer the inclusions, the better.
- Dissimilarity: Inclusions of depression contrast (compared with the precious stone's RI and color) are less visible, and thus, better.
- Location: Inclusions in inconspicuous locations (i.east., about the girdle rather than direct under the tabular array facet) touch on value less. Similarly, a feather perpendicular to the table is less likely to exist seen
Impact on durability
- Type: Unhealed cracks may not but exist unsightly, only also lower a gem's resistance to harm. They are thus less desirable than a well-healed fracture. As already mentioned, tiny quantities of exsolved silk may really meliorate a gem's appearance, and thus, value.
- Location: A crack virtually the culet or corner would obviously increment the chances of breakage more than than 1 well into the precious stone. Similarly, an open fracture on the crown is more probable to chip than i on the pavilion. Inclusions in certain positions may too reverberate, making a single inclusion visible throughout a gem.
Note that cabochon-cut gems more often than not have poorer clarity than faceted precious stone. This is because inclusions are more visible in faceted stones than in cabs.
Cutting ('brand')
The Third C
The function of the cut is to display the gem's inherent beauty to the greatest extent possible. Since this involves aesthetic preferences upon which there is little agreement, such as shape and faceting styles, this is the most subjective of all aspects of quality analysis.
The parts of a faceted jewel. Photo: Wimon Manorotkul
Evaluation of cut involves five major factors (in no item order):
- Shape
- Cutting manner
- Proportions
- Symmetry
- Finish
Shape.This describes the girdle outline of the jewel, i.e. round, oval, absorber, emerald, etc. While preferences in this area are largely a personal pick, due to marketplace need and cutting yields, certain shapes fetch a premium. For nigh colored stones, ovals and cushions are the norm. Rounds and emerald shapes are more rare, and so receive a premium from about 10–20% above the oval price. Pears and marquises are less desirable, and so trade virtually 10–20% less than ovals of the same quality. The shape of a cut gem almost ever relates to the original shape of the rough. Thus the prevalence of certain shapes, such as ovals, which allow greatest weight retention.
Cut style. The cutting fashion (facet pattern) is as well a rather subjective choice. Over again, because of market need, manufacturing speed and cutting yields, sure styles of cut may fetch premiums. The mixed cutting (brilliant crown/step pavilion) is the market standard for cerise and sapphire, while the step (emerald) cut is the standard for emerald.
Proportions. The faceted cut is designed to create maximum luminescence and scintillation in the near symmetrically pleasing manner. Faceted gems feature two parts, crown and pavilion. The crown's job is to take hold of light and create scintillation (and dispersion, in the instance of diamond), while the pavilion is responsible for both brilliance and scintillation. By and large, when the crown height is too low, the gem lacks sparkle. Shallow pavilions create windows, while overly deep pavilions create extinction. Once more, proportions often are dictated by the shape of the rough material. Thus to conserve weight, Sri Lankan textile (which typically occurs in spindle-shaped hexagonal bipyramids) is generally cut with overly deep pavilions, while Thai/Cambodian rubies (which occur as thin, tabular crystals) are often far too shallow.
- Depth percentage: In attempting to quantify a gem's proportions, reference is often made to depth percentage. This is calculated by taking the depth and dividing it by the girdle diameter (or average bore, in the case of not-round stones). The acceptable range is generally lx–80%.
- Length-to-width ratio: Another measurement that is used for non-round stones is the length-to-width ratio. Overly narrow or broad gems of certain shapes are generally not desirable.
If a jewel is cut too shallow, light volition pass straight through, rather than returning to the middle as brilliance. This is termed a "window" (right). In well-cut gems, well-nigh light returns as brilliance (left). Brilliant areas are those showing brilliant reflections. Extinction is used to describe dark areas where petty or no light returns to the eye. Photograph: Wimon Manorotkul
Symmetry. Like any finely-crafted production, well-cut gems display an obvious attention to item. A failure to take proper care evidences itself in a number of ways, including the following:
- Asymmetrical girdle outline
- Off-center culet or keel line
- Off-center table facet
- Overly narrow/broad shoulders
(pears and eye shapes)
- Overly narrow/deep fissure (heart shapes)
- Overly thick/thin girdle
- Poor crown/pavilion alignment
- Table not parallel to girdle plane
- Wavy girdle
Finish. Lack of care in the finish section is less of a problem than the major symmetry defects to a higher place, because it tin can usually be corrected by simple repolishing. Cease defects include:
- Facets practise not meet at a signal
- Misshapen facets
- Rounded facet junctions
- Poor polish (obvious polishing marks or scratches)
Scintillation ('sparkle'). This is an of import gene in faceted stones. A gem cut with a smooth, cone-shaped pavilion could display full brilliance, simply would lack scintillation. Thus the utilise of small facets to create sparkle equally the jewel, calorie-free or center is moved. In general, large gems crave more facets; small gems should have less, for tiny reflections cannot be individually distinguished by the eye (resulting in a blurred advent).
Dispersion ('fire'). This involves splitting of white light into its spectral colors as information technology passes through non-parallel surfaces (such as a prism). While diamonds prove this property to great effect, with most colored stones, their dispersion is too low and the masking result of the rich body color so loftier, that it is not generally a factor. Exceptions are gems such equally demantoid garnet, grandite garnet from Mali and sphene. In gems such every bit these, a weaker torso color can actually exist desirable, making the fire more visible.
Summing up cut. While these guidelines may be useful, one must non become a slave to them. In essence, the cut should display the gem's beauty to best advantage, while not presenting setting or durability issues.If the gem is beautifully cutting, things such as depth per centum or length-to-width ratio matter not one bit. What works, works. The eye, the heed and the centre are the last arbitrators, not numbers.
1 final note about cut. The nigh expensive colored gems (particularly colored diamonds and rubies) frequently feature misshapen proportions and symmetry. This is because the value of the material is so high that the cutter strives to salvage every point in weight.
CARAT WEIGHT
The Fourth C
Weight in gems is calculated in metric carats, where five carats equal i gram. More often than not, as a precious stone'south weight increases, so does the per-carat cost. Such a relationship has long been known, and was first quantified by Villafane in 1572, for diamonds. Today information technology is most usually referred to equally the 'Indian Law' or 'Tavernier'due south Law', and works as follows:
Wtii x C = price per stone
Weight of gem = 5 ct (Wt)
Cost of a 1-ct jewel of equal quality = $yard (C)
5 x 5 x one thousand = $25,000 total stone price
The following shows how the toll of a gem might increase with this formula applied using a $1000/ct base of operations price.
| Weight | Full stone cost |
| 1 ct | $i,000 |
| ii ct | $four,000 |
| 3 ct | $9,000 |
| 4 ct | $sixteen,000 |
| 5 ct. | $25,000 |
| 10 ct. | $100,000 |
Unfortunately, things were not so elementary, even for diamonds in the time of Tavernier. The law could not accurately predict the toll of diamond below 1 ct, and there were also problems with uncommonly large stones. But it does give a full general thought of how prices increase with size.
| Carat psychology |
| In the case of many gems, including ruby and sapphire, psychological (only all too real) toll jumps occur at certain weights. For example, a 0.99-ct ruby-red might be worth significantly less than one which weighs 1.05 ct. The i.05 crimson would be worth more than than i which weighed exactly i.00 ct, as repolishing a one.00-ct stone (or weighing it on someone else's scale) might transport information technology beneath the important ane-ct barrier. Similar psychological weight hurdles are found at the 2, 5, ten, 20, 50 and 100-ct levels. |
 |
| Above. Graph representing the human relationship betwixt toll and quality/weight/rarity. Notation that this is not a linear relationship. Price increases more quickly as quality/weight/rarity increases. Illustration © R.Westward. Hughes |
COLOR COVERAGE
The Fifth C
With gems, we are not dealing with opaque, matt-cease objects of uniform color. Thus it is not enough to simply draw hue position, saturation and darkness. Nosotros must besides depict the color coverage, scintillation and dispersion.
Differences in proportions, inclusions, transparency, fluorescence, cutting, zoning and pleochroism can produce vast differences in the color coverage of a gem, especially faceted stones. A gem with a high degree of color coverage is i in which color of high saturation is seen across a large portion of its confront in normal viewing positions. Tiny light-scattering inclusions, such as rutile silk, can actually amend coverage, and thus appearance, by scattering light into areas it would not otherwise strike. The terminate effect is to give the gem a warm, velvety appearance (Kashmir sapphires are famous for this). Red fluorescence in ruby boosts this even so further.
Color coverage tin be influenced by a variety of factors, including proportions, fluorescence and inclusions. The circular Burmese red spinel at left is strongly fluorescent and the carmine emission adds extra power to the red body color, covering up extinction. With the fine emerald-cut Kashmir sapphire pictured at correct, color coverage is improved by the presence of tiny needlelike inclusions, which scatter light across the stone, thus reducing extinction. This is what gives Kashmir sapphires their unequalled velvety color. Note that both of these gems take colors which are highly saturate, making them highly desirable. Photos: Wimon Manorotkul, John McLean
Proper cut is vital to maximize color coverage. Gems cut too shallow let but brusque low-cal paths, thus reducing saturation in many areas. Such areas are termed windows. Those cut too deep allow light to get out the sides, creating nighttime or black areas termed extinction. Areas which allow full internal reflection will display the near highly saturated colors. These areas are termed brilliance.
Color zoning can likewise reduce color coverage. Ideally, no zoning or unevenness should be present.
Color can likewise be influenced by colour zoning, an unevenness of color. The oval sapphire above shows moderate color zoning. Moderate to astringent color zoning does impact quality, and thus toll. Color zoning is ever judged in the face-up position, in an 180° arc from girdle to girdle, with the gem rotated through 360°. Colour irregularities visible but through the pavilion generally do non impact value. Photograph: Wimon Manorotkul
Pleochroism is noticeable face-up in some gems, such as some tourmalines and iolite. It typically appears equally ii areas of lower intensity and/or slightly different hue on reverse sides of the rock.
The effects of pleochroism can conspicuously be seen in this oval dark-green tourmaline. Forth the vertical axis, a bluish green color is seen, while forth the horizontal centrality, the colour is yellowish green. This is a production of the doubly refractive nature of tourmaline. Photo: Wimon Manorotkul
In summary, a peak-quality jewel would display the hue of maximum saturation across a large percentage of its surface in all viewing positions. The closer a jewel approaches this ideal, the better its colour coverage.
Enhancements
The term "enhancement" is a treatment or process other than cutting and polishing that improves the advent (color/clarity/phenomena), immovability, value or availability of a gemstone. In today'southward gem marketplace, many gemstones have been enhanced past a diversity of methods. Such processes may range from simple heating (such as with tanzanite) to high-tech irradiation (such as blue topaz).
Gems which have not been subject to enhancement are generally worth more than those of the same quality which take been enhanced. For more on enhancements, click hither.Because enhancements affect value, information technology is vital that buyers be provided with full enhancement information when considering the purchase of whatever gem.
Colored Rock Grading: Art or Scientific discipline?
Among the bug of existing colored stone grading systems is that the model chosen is based on diamond. While diamond does share a number of quality factors with colored stones, others are partly or wholly inappropriate. For case, beauty in diamond is largely a function of the textile's brilliance and dispersion ('fire'). Whatsoever inclusions which modify the path of light could be detrimental to a diamond's appearance. Perfect clarity is thus the ideal. Equally described in a higher place, perfect clarity is non necessarily the platonic for ruby and sapphire. While fractures and most other inclusions do have a detrimental effect on appearance and immovability, modest quantities of finely dispersed inclusions (such as exsolved rutile silk) can actually ameliorate a richly colored gem's advent. The watchword here is pocket-size; as well much silk decreases transparency by scattering, reducing color saturation, and thus producing a more grayish color.
Fine precious stones are comparable to cracking works of fine art. Like a painting, to appreciate it, one must view the whole, non just the parts.
Precious vs. semi-precious
In one-time times, gems were oft divided into "precious" and "semi-precious" categories. The precious stones were:
- Diamond
- Ruby
- Sapphire
- Emerald
Semi-precious stones included everything else. While such categories were convenient, they ignored the reality that any precious stone can be inexpensive if the quality is low. In addition, some of the then-chosen "semi-precious" stones tin can cost tens of thousands of dollars per carat (Paraíba tourmaline, for instance). Thus the terms "precious" and "semi-precious" have lilliputian meaning today with regard to value. Today, information technology is more than common to separate gems into either diamonds or colored stones, rather than precious or semi-precious.
PRICING FACTORS
Why they don't ever make sense
Prices of Genuine Jewels
The prices of jewels are not stable. In that location is no police governing their prices, and there is no reason why these prices should not fluctuate with time and place. Each land, each nation carries its own temper. Furthermore, at one time nobles begin to sell them off and at others, to stock them. Stones are plentiful at one time and scarce at another. God grants honour to some and disgrace to others.
al-Biruni, 11th century AD
Kitab al-Jamahir fi Ma'rifat al-Jawahir
One of the great mysteries for the jewel novice is the relationship between toll and quality. In a perfect world, price would straight relate to quality/weight/rarity. Unfortunately, Planet Gem is far from symmetrical. Market place factors tin can have equally much, or even greater, impact on prices as does quality. Prices are influenced by the following factors:
- Quality: Better qualities are more than rare than lower qualities of the same size (see previous section).
- Weight: Bigger stones are more rare, and so more expensive per carat than the same quality of a smaller size.
- Market factors: This is the groovy intangible. Market place factors tin dramatically affect cost.
Market factors
But a few of the market factors that influence price include:
- Market supply vs. demand: Items which are plentiful and/or in low demand will be cheaper than those which are rare and/or in high demand.
- Financial situation of the seller: Sellers who need money will apparently exist more flexible on price. Similarly, those who are non in need are less willing to reduce their price.
- Seller's business overhead: Prices can vary dramatically depending on the seller's overhead. A cup of java purchased by a street vendor may cost merely a few cents; the same cup of java at a v-star hotel in the same metropolis may cost 10–20 times more, due to the hotel'due south higher overhead.
- Buyer'southward financial situation: Buyers whose businesses are prospering are often willing to pay higher prices.
- Buyer's sales prospect: Buyers who have a customer waiting for an item are oftentimes willing to pay higher prices.
- Heir-apparent/seller personal relationship: No ane likes to do business with unhappy or abusive people. When the buyer and seller savor each other's company, they often brand special provisions for 1 another.
- Personal situation surrounding the sale: The author has seen buyers pay above-boilerplate prices for goods for a multifariousness of reasons. These have ranged from trying to impress one's girlfriend, to ownership something just to forbid a competitor from purchasing the same goods.
Influence of lighting on color
Lighting can have a dramatic effect on the appearance of whatever colored jewel. Incandescent lighting (left) is rich in red, orange and yellow wavelengths and thus pushes an object's color in that direction. In contrast, skylight (right) is more than balanced, pushing the color in the contrary direction. (Illustration: Minolta)
With whatsoever colored gemstone, the colour seen depends on the light source used to illuminate information technology. Over time, precious stone dealers have come to rely on skylight for their jewel buying. Its major advantage is its strength, which ruthlessly reveals flaws. The quantity of light coming through even a pocket-sized-sized window is far greater than even the strongest, colour-balanced fluorescent tube (or tubes). Another factor appears to exist the large radiating area, when compared with the most bogus lights.
Latitude may also touch a stone'due south color, but considering skylight is stronger in the torrid zone. As a result, gems bought in the tropics will appear slightly darker when taken to more than temperate climes. It is a slight, only however, noticeable difference. Surprisingly, north skylight (or southward skylight in the southern hemisphere) is actually stronger on cloudy days.
Another factor is the Purkinje shift. In bright light, the eye is more sensitive to red; conversely, in dim light the eye is more sensitive to blueish-violet light. Thus the color of blue sapphires would be slightly enhanced in dim lighting.
The question of north skylight.Due north daylight (skylight, as opposed to direct sunlight) has go the standard, because it produces the least glare, just bullheaded adherence to such gemological dogma is just as bad as blind adherence to religious dogma. If yous live north of the Tropic of Cancer (Europe, North America, Japan, China, etc.), north skylight will provide the to the lowest degree glare year round, considering the sun always passes through the southern portion of the sky. This is particularly true the farther north ane goes. The reverse holds true for those who reside southward of the Tropic of Capricorn (in the southern hemisphere), where the least glare is found using south skylight. Natural light is not abiding in spectral limerick, but varies according to latitude, time of mean solar day, cloud and pollution weather and whether or not one is using direct sunlight or skylight.
The Buddhist temple at Swayambunath, Nepal, silhouetted confronting a deep blue heaven. It is obvious that such skylight would enhance the appearance of blue stones.(Photo ©R.W. Hughes)
Fog in Sri Lanka'due south central highlands. The high moisture content gives the light a grayish cast.(Photograph ©R.Due west. Hughes)
Sunset on Sri Lanka'south western coast. While such sunlight could hands enhance the color of red and yellowish stones, it should be noted that direct sunlight is rarely used for examining gems. (Photo © R.W. Hughes)
Typically we use skylight, instead. Such skylight is really more than blue early and late in the mean solar day. Thus blue sapphires will look meliorate at those times. Conversely, when viewed with skylight, rubies volition look all-time effectually midday, because the skylight is less blue.
What about those who alive in the torrid zone? If they are north of the equator, north skylight is all-time, except May–July, when southward skylight is preferred. For the torrid zone south of the equator, south skylight is all-time, except from Nov.–January., when north skylight is preferred. And if you live right on the equator, utilise due north skylight from Oct.–February., and due south skylight from April–August. During March and Sept., either north or south skylight tin exist used.
Fourth dimension of day. Even skylight changes throughout the twenty-four hours. Generally speaking, rubies (and other red stones) await all-time during the midday hours. Sapphires, in contrast, look best in the early morning or belatedly afternoon. If you lot are buying, this means that rubies should be purchased early on or belatedly in the day, while sapphires are all-time bought near midday, thereby preventing a surprise when the stone is examined under some other lighting status.
The above is in contrast to what is often reported. While direct sunlight is far more red at sunrise and dusk, the skylight is actually more blue. Since we use skylight, not direct sunlight, to illuminate gems, blue color will be enhanced early on and late in the day. Similarly, the skylight at noon is less bluish, thus enhancing the color of rubies in the middle of the day.
Weather and pollution. How might clouds or pollution affect color? Heavily-polluted or cloudy skies will result in more grayish (less blue) skylight, thus improving the advent of rubies (as opposed to sapphires).
Bogus lighting. Some blazon of bogus calorie-free is obviously the respond to neutralize the above factors. Many dealers today do their ownership under special daylight lamps designed to simulate true due north daylight, with a colour temperature of approximately 5000–6100° Kelvin. Generally speaking, while their color remainder is similar to due north daylight, the fluorescent tubes used endure from depression light output. A 20-watt fluorescent daylight tube at a distance of 30 cm produces about 1000 lux of illumination, while a northward-facing window in Bangkok averages 6000 lux.
Viewing geometry & background
Gems are designed to be mounted in jewelry and viewed from predetermined angles. This is generally face-up, with the precious stone viewed in a 180° arc from girdle to girdle. Thus it is only logical that all quality determinations be made with the naked eye under the aforementioned viewing geometry. Information technology is important that the jewel exist rotated through 360° in the girdle plane, and then that its appearance is seen from all angles, merely every bit it would be when mounted in jewelry. To ensure reproducibility and repeatability, a standardized calorie-free source against a standardized, neutral background (white is best) at a standardized distance should be used. The practise in diamond grading of judging body color through the pavilion facets is madness, and has no place in colored stone grading.
Groundwork checks
When you are examining a colored gemstone, human activity like a cop – always exercise a background check.
The color of the groundwork against which a gem is examined tin accept a major effect on colour. Which is why wily Burmese and Thai miners traditionally offering up rubies to buyers on brass plates or yellow table tops. The yellow groundwork colour countesent in ruby, making the gems announced more than red. Yellow cellophane-lined rock papers or brass tweezers serve the aforementioned purpose. Don't exist a sucker. For judging color, a plain white groundwork.
In a higher place, rubies and red spinels are typically traded on contumely plates in Mogok, Burma. Photo © R.Due west. Hughes
SUMMARY OF QUALITY
Again, the appearance of a colored gem is a combination of many dissever factors, each of which is related to, and afflicted by, the others. It is precisely the complexity of these intertwined relationships that has bedeviled previous attempts to quantify quality. And still, every time a dealer buys a gem, a quick mental analysis is fabricated, commonly within seconds. In grading any gem, one must exist cognizant of, simply not become lost in, the details. When all the minutiae has been pored over ad infinitum, advertising nauseam, accept a pace back and simply look at the precious stone. In the age of loftier-powered microscopes this may constitute a radical concept, simply i which is necessary.
Source: http://www.palagems.com/quality-4cs