1/Colored Stone Price Factors in a Nutshell
The following factors can affect the prices of colored gems:
Color
Cut quality (proportions and finish)
Stone shape and cutting style
Carat weight or stone size
Clarity (degree to which a stone is free from flaws)
Transparency (degree to which a stone is clear, hazy, cloudy or opaque)
Treatment status (untreated or treated? type and extent of the treatment)
Distinctness of phenomena if present (e.g., stars, cat's-eyes, alexandrite's color change, opal's play-of-color)
The pricing of colored gems is also determined by market factors such as demand, form of payment, buyer's credit rating, amount purchased and competitors' prices. Sometimes you can find the same dealer selling a stone of higher quality for less than one of lower quality. This is because the rough for the higher quality stone may have cost less. Or, the rate of currency exchange could have been more favorable at the time the dealer purchased it. Therefore, you should not assume that higher price necessarily means higher quality. Conversely, lower price is not necessarily indicative of a deal.
Why the 4 C's isn't an Adequate Pricing System
You may be surprised that there are more than four price factors if you've heard about the 4 C's of color, cut, clarity and carat weight. The 4 C's system of valuing gems is a clever, convenient way to explain gem pricing. The problem is that it causes consumers to overlook the importance of cut quality, transparency and treatment status.
If you see a mini gem-lab report stating that the shape/cut of a gemstone is round brilliant, you may assume that this tells you everything about the cut of stone when in fact it doesn't. The quality of the cut is important and it's a separate price factor from shape and cutting style.
If you're not informed about gem treatments, you may assume, for example, that two equally attractive jade stones should be priced alike. However, if one is dyed or bleached and the other is of natural color, their prices should be quite different. Chapter 2 describes the ways in which gems are treated.
If you're comparing a cloudy stone to a transparent one, be aware that transparency can have a significant impact on each stone's value. Transparency and clarity are often interconnected, but they're not the same. A stone can be transparent like crystal yet have a low clarity. Likewise a stone may be flawless, yet be cloudy and milky in appearance.
Price Factors Explained
COLOR: It can be broken into three components:
Hue: Basic spectral colors like those in a rainbow such as blue, green and bluish green. Brown, black, gray and white aren't hues because they're not part of the color spectrum.
Tone: Amount of color, the degree of lightness or darkness
Saturation: Amount of grey or brown masking the hue. This component is also called "intensity" and "chroma" depending upon the color system you're using. Stones with a high color saturation have hardly any grey or brown masking the hue.
Gem dealers often disagree on what is the best hue and tone for a given gemstone such as sapphire or emerald. They agree, however, that for most gem varieties, the less brown or gray that is present, the more valuable the stone. For example, the center ruby in figure 1.1 is worth much more than the brownish rubies on each side.
If you're buying a gemstone for yourself, it doesn't matter what color you choose as long as you like it and the color looks good on you. However, when buying gems for resale or as gifts, find out what hues and tones gem dealers prefer. Chapter Four describes the preferred colors for various gem varieties. Usually the strongest and richest colors are the most valuable. Very light and very dark stones typically cost less.
When judging color:
Clean the gemstone with a soft cloth if it's dirty.
Rotate the stone and examine it from various angles, keeping in mind, however, that color is judged in the face-up position.
Look at the stone under different types of light such as an incandescent light-bulb, fluorescent light and daylight. Top quality stones look good under all types of light. Daylight equivalent light is the standard used for gem grading.
Examine the stone against a variety of backgrounds-white, black and against your skin.
Examine the stone for color zoning-the uneven distribution of color. When the color is uneven or concentrated in one spot, this can sometimes decrease the stone's value. Obvious color zoning is most serious when visible in the face-up view of a stone.
Compare the stone side by side with other stones of the same variety. Color nuances will be more apparent.
Fig. 1.1 A ruby with good red color flanked by two rubies which have a much less valuable color-brownish red. Rubies from Andrew Sarosi; photo © Renée Newman.
Fig. 1.2 Tanzanite without a window. Fig 1.3 Tanzanite with a window. Photos © Renée Newman.
CUT QUALITY: A well-cut gemstone displays brilliance and color throughout the stone (figure 1.2). It shouldn't have an obvious window-a pale, washed out area in the middle of the stone that allows you to see right through it (fig. 1.3). In general, the larger the window, the poorer the cut.
To look for windows, hold the stone about an inch or two (2-5 cm) above a contrasting background such as your hand or a printed page. Then try to look straight through the top of the stone without tilting it. The stone has a window if you can see your hand, the print or the background through the center of it.
When buying a gemstone, be sure to look at its profile. The side view will show you if the stone is too deep for the mounting, too shallow or too bulky. Diagram 1.1 shows you the profile of a well-cut colored gemstone and defines terminology related to gemstone cut. Figure 1.4 is another example.
Figure 1.5 illustrates a poorly proportioned tanzanite. This stone was cut to maximize weight from the rough at the expense of beauty. The shallow pavilion (bottom) reduces brilliance and creates a large window. The high crown (top) and thick girdle (rim around stone) add unnecessary weight, which increases the price of the stone. Faceted gems are usually priced by weight.
Diagram 1.1 Profile of a mixed-cut colored gemstone.
Copyright 1978 by American Gemological Laboratories.
Fig. 1.4 Profile of a well-cut tanzanite. Fig. 1.5 Tanzanite with a crown that is too high, a pavilion that is too shallow and a girdle that's too thick. Photos © Renée Newman.
When judging cut, consider, too, the quality, complexity and originality of the faceting (arrangement of small polished surfaces called facets). Some of the best faceting is done on low- and medium-priced gem material such as aquamarine, garnet, quartz, tanzanite, topaz and tourmaline. The faceting and proportioning of more expensive gems like emeralds, rubies and alexandrites is often less precise because the higher cost of the rough leads many cutters to be more interested in retaining weight than in maximizing beauty. For a fuller discussion of cut evaluation, consult the Gemstone Buying Guide by Renée Newman.
SHAPE & CUTTING STYLE: A gem's shape is its face-up outline. The most common gemstone shapes include the round, oval, square, triangle, pear, marquise, heart and cushion, a squarish or rectangular shape with curved sides and rounded corners. Gems can be any geometric shape or they may resemble objects such as animals, bells, stars, the moon, etc.
Gems can also be cut as abstract freeforms. Cutters try to select shapes and cutting styles which allow them to emphasize preferred colors and brilliance, minimize undesirable flaws, and/or get the maximum weight yield from the rough. In small calibrated sizes, there is a tendency to cut what jewelry manufacturers want, even when some shapes cause a greater weight loss. Standard sizes and shapes are required for mass-produced jewelry.
The effect of shape on price varies depending on the seller, the gem variety, the stone weight, the stone quality and the demand for the shape. A high-quality, one-carat round ruby, for example, may cost 15% to 20% more than one with a cushion shape. In small sizes and low qualities, the shape may have no effect on the price. The subject of shape pricing is too complicated for this book. Simply remember to compare gemstones of the same shape and cutting style when evaluating gem prices.
Cutting style refers to the way in which a stone is cut or faceted. An oval-shaped stone, for example, may just be rounded as a cabochon (unfaceted stone with a dome-shaped top and either a flat or rounded bottom) or it may have facets (polished surfaces with varying shapes) that are arranged in different styles. There are three traditional faceting styles:
Step cut: Has rows of facets that resemble the steps of a staircase. The facets are usually four-sided and elongated, and parallel to the girdle....
