The Best Light for Buying and Selling Gems

When you buy a colored stone at a jewelry show, does its color look different when you get it back home? It’s all in the lighting, gem dealers say.

“Color is the most important feature of a colored stone, and gemstones get color from light,” says Dana Schorr, owner of Schorr Marketing, a gem wholesale business in Santa Barbara, Calif. Therefore, the light used by gem buyers and sellers “is most important for your perceived value,” he says.

For many years, Schorr has been buying gems in Kenya and Tanzania and cutting them in Sri Lanka. He sells domestically as well as in India, Thailand, Hong Kong, and Japan. With trading environments varying from one country to the next, the lack of universal lighting standards is extremely frustrating, Schorr says. When color appears different from one location to the next, it’s more than a mere inconvenience for those in the business of buying, cutting, and selling gems. A stone that appears to be one color at the exhibit booth but a different color in your store can mean a loss in profit.

Why they look different. Several factors come into play. First, gems look different when viewed under incandescent and then fluorescent light. In tanzanite, for example, the hue changes from purple to blue. With this in mind, many jewelers examine all tanzanites under two different light sources. Second, many gems are metameric. This means that two stones that match each other under one halogen light source may not match under a different-temperature halogen bulb, a fluorescent bulb, or even natural daylight. Third, numerous colored gems are pleochroic, able to split any white light into two or three different colors. Gem artists orient the face-up position of the gem to reveal the preferred pleochroic color. Tanzanite has three pleochroic colors: blue, violet (the hue between blue and purple), and a very faint brown. The orientation of the cut will affect not only its face-up color, but also its color change and the degree to which its color matches that of its mate.

Trade show lighting. Color-matching problems are most evident at trade shows. There you find a variety of lights from one booth to the next—halogen, metal halide, incandescent, and fluorescent. You don’t have this problem in the diamond section, since a standard light source is used for color-grading diamonds. Retailers can return home confident that the diamond’s color they saw at the show will be the same back at the shop under the same standard light. That’s not the case with colored stones.

“The colored stone industry, unfortunately, has almost no standardization on the subject of lighting,” says Martin Chung, a Graduate Gemologist and master gem cutter who is president of Gemological Lighting Concepts in Los Angeles. “Lighting standards are prevalent in many industries. Automobile manufacturers, graphic artists, the textile industry, and even tobacco graders have strict government or self-imposed guidelines for color communication and evaluation. So when an automobile component is fabricated in Mexico, manufacturers utilize lighting specifications to ensure that their color will correctly match the final product being assembled in Detroit. Ironically, gemstones, unlike cars, vary wildly in price depending on their color.”

Most jewelry trade show venues, including those at Las Vegas, New York, and Tucson, are lit by mercury vapor lights. This lighting wreaks havoc with gem color, especially red gems. What can the gem dealer do? “We try to flood the booth with halogen,” says Josh Hall of Pala International in Fallbrook, Calif. “We have 18 lights, about 900 watts, to try to overcome that. And if anyone is buying red at any of the shows, I tell them to take it outside.” That may be a good temporary solution, but this too may cause confusion. Gems viewed in daylight usually will not look the same as they will in your store.

To eliminate lighting problems, smart trade show shoppers bring a familiar stone from their inventory or a swatch of clothing to match. This is better than bringing nothing at all, but “even having master stones won’t eliminate the problem,” says Schorr. Master color samples don’t work unless you’re using the same lighting both in your store and where you are buying.

By the numbers. To understand the relationship of gem color to lighting, you need to know two numbers: the color temperature (CT) and the color rendering index (CRI).

CT is a simple scale that quantifies the color of light in degrees Kelvin (K). Chung explains the theoretical concept behind the measurement: “This measurement has no relation to the temperature of the light source itself. But to oversimplify its meaning, the higher the temperature, the higher the quantity of blue that is present in the light. Conversely, the lower the CT, the higher the quantity of red.”

Standard incandescent light bulbs operate at a color temperature of 2900K, a yellowish-red. “Warm White” fluorescent tubes are generally rated at 3500K (reddish-yellow). “Cool White” is rated at 4100K (yellow-green). The “Daylight” tube is between 5500K and 6500K (slightly blue). Actual north daylight is said to be approximately 7500K (also slightly blue). Average sunlight is approximately 5000K (green-blue).

While all of these lights are classified as “white lights,” in fact true white light is between 5500K and 6500K. Outside of that range, each light produces a dominant color in the visible spectrum. Schorr notes that it’s possible to juggle your primary colors for a particular Kelvin temperature. For example, 5500K lights could cast a reddish or a bluish glow. When you’re comparing lighting specifications, spectral output curves provided by the bulb manufacturer show color spikes that cause the lights to have a predominant hue, such as blue, red, or yellow.

The CRI measures the degree to which a bulb is able to display color at a given color temperature—the closer to 100 the CRI, the better the color display, according to Chung. However, Schorr points out, “CRI numbers for lights above 5000K are calculated by comparing the light output to actual daylight. But with lights under 5000K, the CRI numbers are calculated comparing against halogen light.” Thus, a light above 5000K may have a lower CRI than a 4100K halogen or metal halide, but it may actually have better color rendering.

Lighting vendors to the rescue? There’s little agreement, even among those in the lighting industry, as to what light should be the standard for viewing colored stones. Gem dealers and retail jewelers are left to their own discretion. Joe Stevenson of Stevenson Lighting in Santa Maria, Calif., reportedly has sold 250 dealers the new SoLux halogen bulb for the JCK Las Vegas show. The SoLux halogen is available in three different CT-rated lamps: 3500K, 4100K, and 4700K. The 3500K lamp, Stevenson says, is good for artwork, the 4700K is appropriate for displaying diamonds, and the 4100K is suitable for colored gems.

But another vendor, George Halvatzis, owner of Econo-Lite in Jersey City, N.J., downplays halogen and Stevenson’s color temperature ratings. He’s hot on metal halide lamps. “We have customers complaining that the halogens are too yellow,” says Halvatzis. While halogen has been a store standard for the past decade, according to Halvatzis, the industry seems to be shifting to halide. “The 4100 Kelvin bulbs are fabulous for diamonds, platinum, and silver. The 3100 Kelvin bulbs are good for colored stones and pearls.”

“Everybody likes something different,” notes Mike Lahijani, owner of Future Designs, a lighting company in Miami, who sells the new LUX Millennium metal halide. And with no agreement on a standard light, there’s no consistency in the color appearance of gemstones from one store or trade show booth to the next.

High-lighting your inventory. Some companies know all too well about lighting and use this information to their advantage by having both “buying lights” and “selling lights.” They use poor color-rendering lights for buying and color-exaggerating lights for selling. As a buyer, you must be aware of the lighting situation when you’re examining gems. If the light is very red, your rubies will look too good. If the light is very blue, your sapphires will look better than they should.

As a reputable retail jeweler, you want to present the gem in fair lighting to your customer, showing off the beauty of the gem without adding unnatural color. Make sure your lights don’t overplay color output. Otherwise, the gem won’t look as good in your customer’s home as it did in your store.

Lighting is purely up to the store designer and owner, says Ruth Mellergaard, president of GRID/3 International Inc., a New York firm that designs store interiors. “Christian Bernard Jewelers in Secaucus, N.J., originally went with metal halide and some tungsten halogen,” says Mellergaard. Since then, they’ve changed their minds and gone totally metal halide. “They like the incredible whiteness and brightness,” says Mellergaard. Other jewelers think the halides are too white. Managers at Braunschweiger Jewelers in Morristown, N.J., for example, like the warmth of the tungsten halogen lights.

While at first it may seem a good idea to separate your colored gems into designated areas, this may not be possible. “Colored stones, in truth, are not emphasized as much as diamonds,” says Mellergaard. Colored stones are sold all over the store, and most jewelers will move their merchandise every so often. Maintaining the lights is another key issue. A jeweler typically will spend $2,000 to $4,000 a year on replacement bulbs. Whoever replaces the lamps must know the proper positioning. If there are incorrectly positioned replacement bulbs, you will soon notice that something is wrong with your store’s lighting.

One way to emphasize gems, suggests Mellergaard, is to use tungsten halogen spots (3500K), which are warmer and less intense. Consider having cases devoted to individual colored gem varieties, especially if colored gemstones get a lot of emphasis in your store. But with no additional lighting, the store will look too dark. “Customers want a brighter-looking store,” says Mellergaard. “[Jewelers] need to add some general lighting as well.”

The color of your store—including the paint on the walls and the color your lights produce—affects not only how your gems appear, but also the way your customers look and how they feel about purchasing gems. If your lights enhance the gems but make the customer look pale and unhealthy, she may not want to buy what you’re selling—and she may not even want to return to your store.

Mellergaard and Chung recommend that store owners and designers investigate the different looks of all the lighting available. Also consider the customer’s reaction to the light. Customers may feel that the lights in the store make everything look great, but when they get home they’ll be disappointed because their jewelry doesn’t look as pretty as it did in the store.

“When dealing with luxury items such as jewelry and art, lighting for correctly presenting your wares is of paramount importance,” says Chung. “Currently, with the wide variety of available light sources, it is significantly easier to manipulate light to your needs. This will help you take command of your environment and consequently create a greater sales potential.”

Showing Colored Gems in Their Best Light

Certain gems look best when displayed in a particular form of lighting. Emeralds, for example, are often illuminated with standard incandescent light bulbs high in red content. Green and red are complementary colors that, when combined, create brown. Yellow-green gemstones look best under a 4100K light bulb with a spectral output centered on yellow-green. This bulb, however, is the worst choice for red, violet, and purple stones. These are the complementary colors to the output of the bulb and will therefore create brown.

Ideally, you should segregate gems by color. Place warm hues—red, orange, yellow—in one area using a warm, daylight-equivalent light source (3000-3500K). Set cool-hued stones—green, blue, and violet, as well as white and black pearls—in another showcase with a cool daylight source (4500-5000K). For example, emerald, peridot, tsavorite, or other predominantly green stones appear best when subjected to green- or blue-centered daylight-equivalent bulbs at around 4500-5000K. This form of sympathetic lighting—matching the differing colors of daylight equivalents to the color of the item being displayed—is the cornerstone to maximizing the beauty of your gem creations.

It’s generally detrimental to cast a yellow hue on any gemstone (the exceptions are golden pearls and yellow diamonds and sapphires). For ruby, blue sapphire, and most other varieties, yellow is an undesirable modifier. A high yellow content also will make scratches on metal and stone more visible.

Lighting for Bench Jewelers

Bench jewelers and color graders require flat, even, non-glare lighting. A high-quality set of fluorescent ceiling tubes with a color temperature of 4100K (standard “Cool White”) with a color rendering index (CRI) higher than 80 is ideal. (On a scale up to 100, the higher the CRI, the better the bulb displays color at a given color temperature.) This illumination is the equivalent of natural daylight, creating an environment in which your jeweler can be more productive and make fewer mistakes.

Keep in mind that fluorescent tubes generally have a lower CRI than that of halogen bulbs. Most commonly available hardware store tubes range from 60 to 70 for cool whites and 75 to 82 for daylight equivalents.

Avoid using a light that’s too low in yellow content. This makes scratches and pits more difficult to see. Worse, it leads to eyestrain and restlessness for your bench jeweler. Although point sources such as standard light bulbs and halogens are fine for final inspection, you should generally avoid them. They create glare on the surface of the piece and cause eyestrain over prolonged periods.

Information provided by Gemological Lighting Concepts

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