Examine Gemstones for Color - Pitfalls

Intricacies of Color Examination

So you know the various parameters essential in describing a stone. Now you take a few gems and try to examine their color. But you will face problems that you won’t have even thought of. Better educate yourself on those matters.

Here’s the first – the hue and tone of a stone, that is, its perception, can depend on any number of situational factors – the kind of light that you examine it in, the kind of setting the stone is in, the kind of background you have in your examination room, and even the color of the shirt you are wearing at that time. That’s why it’s so hard.

Here’s the funda behind it – a red object looks red because it absorbs all wavelengths of the light that falls on it except for the red ones. So the red ones are reflected and reach our eyes and we perceive the thing as red. Now if the light that is being used for, you know, seeing is not sunlight, but some other kind – such as fluorescent or incandescent light, then the intensity of different wavelengths is not the same. What that means, in English, is that fluorescent light has more blue in it than red, and incandescent light has more red and orange than colors on the blue side.

So a Ruby will look redder under the light of a bulb, and a Sapphire that looks a lovely blue in daylight will turn purple under incandescent light. The same principle is used in setting stones. So, if an Emerald is mounted in a box-setting instead of the standard four-prong, the shadowing effect of the walls will make it look deeper. What we need to learn is not to be fooled by such tricks played by our eyes.

Another issue related to this is the color-change in stones. Stones happen to look one color in daylight and quite another in incandescent light. Sapphires, Spinels and Garnets hardly do that, but there are special ones, such as Alexandrites which show a bluish-green tinge in daylight and turn deep-red under incandescent light. Many color-changing synthetics are sold as Alexandrites. You must prepare yourself against such charades.

Yet another issue is zoning. There are certain stones that naturally occur in a state of complete state of colorlessness, except for a layer or two. If cut in such a way that this layer is parallel to the table, the whole stone will look the same color. Some other stones have multiple layers of color, which, if the stone is properly cut, are very difficult to notice. Saturation and uniformity in color are very important in deciding the price. In such cases, you might be fooled into paying more than what the stone is really worth.

Gems have another property known as fluorescence – the ability to produce visible colors from ultraviolet light. Light has many components other than the visible ones – almost all of you must have heard of ultra-violet light (most as the cause of sunburns). Now this effect may make us see colors that are not a part of the stone’s true color characteristics. A perfect example is Burmese Rubies. These stones look red under short-wave ultraviolet radiations and a very strong red under long-wave radiations, thus showing red under daylight (because it has ultraviolet radiations). This effect only increases the stone’s value, but it’s a complication nevertheless than needs to be acquainted with.

I hope these keypoints shall help you in accurate evaluation of Gemstones.