To most people, rubies are red, violets are blue, but to the savvy stone dealer that’s not always true. Though emeralds come in many shades of green and each may have its own attraction, some of those greens attract greenbacks for more readily than others.
What makes the green is not just the object itself. Ask someone in the printing industry. Ask someone in the textile industry. Ask someone in the photo industry. Those in the know appreciate that a vital piece of the color pie is the light that’s used to illuminate it. And if you plan to be handling colored gemstones, be it as a dealer, jeweler or consumer, a knowledge of lights and their effects on color is a definite plus in your favor.
Humans (and other primates to whom I have spoken) often assume that all light sources of day-to-day life are essentially the same. Unfortunately, this is not the case. Sunlight, fluorescent tubes, incandescent bulbs and candles all possess subtle, but important, differences. To understand those differences, and how they impact the appearance of a gem, we need to know a little bit (just a very little bit) about color and its perception.
What is Color?
White light, such as from the sun, is actually a mixture of violet, blue, green, yellow, orange and red. That this is true can be seen anytime you look at a diamond. The diamond, just like a prism, splits white light into its individual parts. Jewelers call this “fire;” the scientist calls it dispersion.
So why are some objects blue, while others red, green, etc.? The reason is because colored objects do not freely and equally return all colors to the eye. If they did, they would no longer be colored objects: they would be white or colorless. For an object to have color in the first place, it must block some colors and let others pass. The colors that get blocked are said to be absorbed. The ones that collectively get passed are perceived as the object’s color.
Light Sources
Take an orange (the fruit), for instance. In the simplest terms, an orange has an orange color because its skin reflects orange light back to the eye, absorbing all other colors. But for this to occur, a white light must serve as the illuminant. If a blue light source is used instead –that is, a lamp which only emits blue light and no other colors—then the orange would appear black; the orange absorbs the blue light, and at the same time lacks the opportunity to reflect orange light back to the eye.
The bottom line is that objects which normally show color may entirely lack color if a color-deficient light source is used.
Although sunlight and various other lights may appear white, subtle differences in the balance of their component colors can have a dramatic effect on the way they render object color. For example, incandescent lamps contain a lot of yellow-red components. So called cool white fluorescent lamps have more in the way of blue components. The color composition of natural daylight depends (among other things) on whether we are talking about direct sunlight –in which yellow tends to reign—or skylight, which is definitely slanted towards the blue. The color of a yellow, orange or red object will be accentuated when seen under the incandescent lamp or under most phases of direct sunlight. Similarly, a blue, green or violet object is best accentuated under the cool white fluorescent light or skylight. In both cases, the respective light sources give the objects maximum opportunity to reflect to the eye the “normal” color one expects to see.
Getting Down to the Nitty Gritty
Most people in the gem trade, and perhaps some consumers to boot, know that stones look different – sometimes better, sometimes worse—depending on the lighting. The wise gem trader makes the most of the knowledge, turning it into profit.
Let’s now give a thumbnail sketch of some of the lighting techniques used by people in the gem and jewelry trade. Several of these techniques may aptly be labeled tricks-of –the-trade. At the same time, I will offer a few practical suggestions on the effective use of artificial lighting arrangements.
First of all, it’s important to note that when buying and selling stones, traders use either natural daylight or an artificial light source, depending on circumstances. Each type of lighting requires its own special approach for it to be utilized effectively.
Getting Down to the Nitty Gritty
Many dealers use natural daylight when buying and selling stones. The main advantage of natural light is that it’s free. The disadvantage is that gemstones do not always look the same under it. And there is a reason for this: as we have already seen, an object’s color depends on the properties of the light which illuminates it; however, natural daylight lacks constant properties. Such factors as the time of day, weather conditions, atmospheric pollution and even latitude cause constant changes in the strength and composition of natural daylight. These changes in turn affect the color appearance of gemstones. This is why a stone purchased in Bangkok may look darker when viewed under the skies of northern Europe or the USA. It is also the reason why some ruby and sapphire traders limit their business activities to certain times of the day.
Fickle as natural daylight is, the seasoned gem buyer can use it to full advantage. One trick-of-the-trade is to buy when the light is bad and sell when the light is good. The idea here is to buy stones when lighting conditions are least complimentary, as long as the stones look OK. The buyer then gambles that these same stones will look even better (=more valuable) under more favorable lighting. “More favorable” means the kind of lighting the buyer uses when he later sells these stones.
So, why not just buy gems under good lighting conditions in the first place? One reason NOT to do so has to do with bargaining: when lighting conditions are less than optimum, a buyer has the chance to argue that the stones are “overpriced” for their color quality.
To minimize risk, a buyer carries a master stone set for making color comparisons. If he is prudent he will have examined each master stone under varied natural and artificial lighting arrangements. The master stones he packs around include the quality grades he normally deals in. The masters give him some idea of what the comparison stones –i.e., the stones people want to sell him—will look like under these other lighting conditions.
There are different ways to go about selling when the light is good. The oft’ used trick is to utilize complimentary lighting whenever possible. For instance, let’s say you happen to be selling to other dealers who prefer examining stones with natural daylight. During the early morning hours, red, orange and yellow stones look a little better when viewed near a window facing east. If it’s late afternoon, opt for a window facing west. Blue and violet stones look best during these same times, but at a window facing north, if you are living north of the equator.
Making the Most of Artificial Lamps
What if you live ON the equator? What if it’s night time? For that matter, what if you are doing business in a windowless office? Even if you have windows, it’s mighty difficult to control the direction they face. It’s equally difficult to remove neighboring, overshadowing buildings which can block light and otherwise cast funny reflections into the office. Situations like these call for artificial lamps –but not just any artificial lamp.
If you are a dealer, equip your office with an array of suitable daylight-type lamps. Some of the fluorescent models do a reasonable decent job of simulation natural light. When talking to lighting vendors about daylight models, make sure to ask them for specification sheets. Though there are reasons to prefer certain daylight-lamp models over others, here are a few guidelines to work with:
1. The specifications should indicate that the lamp has a color temperature somewhere in the range of 5000-6500. Color temperature refers to the color appearance of the lamp when it’s turned on. A color temperature of 5000 means the lamp looks very white, while 6500 corresponds to a slightly bluish appearance.
2. The lamp must have a color rendering index (listed on the specification sheet as either CRI or Ra) of 90 or more preferable 95+, Color rendering index indicates how well the lamp renders object color as compared with some standard illuminant of equal color temperature. An index of 100 means perfect color rendition compared with the standard; 90 means the rendition is 90% as good as that of the standard, etc.
3. Have enough lamps in the office to provide reasonably strong lighting conditions. Remember, natural daylight, even on an overcast day, tends to be much stronger than the light cast from one or two fluorescent lamps.
If you are a retailer, you probably want lamps which enhance the appearance of gems and jewelry. Most retailers seem to share that predilection, though the lamps they buy sometimes fall short of the objective.
Look at the display windows of some retail outlets and you will see high intensity incandescent lamps beaming down over everything. Such lamps make rubies book great, but blue sapphires are unwittingly rendered as dark as black onyx. One cure for that malady is to use incandescent lighting for red, orange and yellow stones, and cool-white or daylight fluorescent lighting for blue, violet and green stones. Yet a better approach is to use artificial daylight lamps for everything. Sure, the rubies on display will not appear super-enhanced, but there is something to be said for honesty: consumers may appreciate it if their ruby ring does not change color when they step out of the store. The idea of honest lighting could even be turned into a potent marketing point. Thai isn’t as novel as idea as it may sound, inasmuch as several retailers in the eastern USA and in Singapore have started using that same marketing approach –and successfully, I might add.
Checking the Stone under All Lighting Conditions
When buying stones, why not see how they look under various kinds of natural artificial lights? After all, some customers only don their jewels in the evening, more often than not under incandescent lighting. Other customers will wear jewelry at work, which frequently means an office illuminated with fluorescent lamps. Some dealers have carved a nice little niche by first finding out the “wearing habits” of their customers, then seeking stones that best suit those habits: i.e., stones that hold their color well under the lighting conditions in which they will be worn. It’s an approach which has proved profitable for certain dealers. Now it’s time to take a look at how one goes about spotting stones to cater for these special needs.
As a case in point, let’s say you enter an establishment and are shown a stone which particularly strikes your fancy. If you are a typical dealer, the first things you do is walk to the closest window and assess the stone there. However, you also want to know how that stone would look in dim lighting conditions (perhaps you are thinking of selling it as a night stone). So, you hold the stone just under a table and reassess it there. Next you want to know how it looks in incandescent lighting, which is the kind of lighting used at evening in most homes. First, place the stone just under the table in order to cut back on any fluorescent ceiling illumination. Then, shine your penlight on it from a distance of about 4-6 inches. Since penlights are incandescent, you now have a fair idea of what the gem would look like in a room lit entirely by incandescent lamps.
The main concern is how well does the stone hold its color under varied lighting conditions.
The idea of buying stones tailored to accommodate the lighting habits of customers offers plenty of room for experiment. It is an approach that is imminently suitable for smaller traders wishing to carve the aforementioned niche.
Just Any ’Ol Light Won’t Do!
There is no denying that illumination greatly influences the way we perceive the color appearance of gemstones, and that different kinds of lights can effect sundry (and often profound) changes in that appearance. This makes lighting a real dollars and cents issue which should not –pardon the pun—be taken lightly.
As this article has hopefully shown, natural daylight and artificial light sources can each be used in positive ways towards maximizing sales. Regardless of whether you are a wholesaler, a retailer or a consumer, a sound knowledge of lighting techniques will put your buying and selling practices on firmer grund.1
Some Postscript Commentary
In an ideal world, there would be one standard artificial light source used internationally for buying, selling and grading gemstones. Stones would the look the same to everyone, irrespective of the myriad factors which make natural daylight so fickle and artificial lamps differ from one model to the next.
The author strongly believes that a standard and universally accepted lighting arrangement is not just a pipe dream, but something which can and will eventually happen. A practical and cost-effective candidate for this arrangement is a daylight lamp which represents, as faithfully as possible, one phase of natural light. The Asian Institute of gemological Sciences in Bangkok is currently experimenting with various lamps in the attempt to realize this “lighting ideal.” Readers of JewelSiam will be kept posted on new developments in this field.
1Those wishing to explore this subject in greater and more technical detail are referred to the following articles:
1. Sersen, William J. Buying and Selling Gemstones –What Light is Best? (Part I). Gemological Digest. Vol.2, No.4 (1989).