Color and Gemstones

Color IS in the eye of the beholder. People see color differently depending on many factors including eye color, geographic location, atmospheric conditions, time of day and altitude. We will take the most common differences and explain how they affect the way we see color in gemstones.

Purkinje Shift

The Purkinje Shift is the name of the phenomena that states the human eye has the ability to perceive color according to the amount of light that hits it .

Dimmer light fires more of the blue wave length which means that blues will seem more vivid, while more intense light will fire more of the red wave lengths which makes red more vivid. So: blue sapphires are better seen in dimmer light and red rubies in brighter light. Alexandrite, having a Refractive Index (RI) between that of Emerald and Ruby, shows its green coloration best in bright, indirect light and the Red/Purple coloration best under dim incandescent light with warmer tones.

But wait- a second factor that affects how we see color is that different eye coloration (blue, brown, hazel etc) significantly sees color in differing spectral hues. Blue eyes can differentiate over 30% more hues than dark color eyes. Therefore, when a seller in Asia with dark eyes picks out a gem and describes its hue, a buyer in a European country who might have lighter or blue eyes will see the same gem in a different hue. Add in the retail buyer and the difference in perception of color can be even further from the original described hue.

A third factor in seeing coloration in gemstones is atmospheric condition. Hot, high, dry and sunny locations (such as Jaipur, India) shows intense coloration; and cool, low, humid and cloudy locations (such as the coast of Thailand) show coloration as darker and drabber.

Most agents send photographs of their gems to their purchaser. And most sellers take pictures and list the pictures on their websites or in eBay or in a paper advertisement. Another factor to color is the fact is that a camera ‘sees’ light and color as static and that computer monitors have different settings and basic color differences. This does not allow the color of a gem such as alexandrite (that has three axis and shows color a bit differently according to the axis) to be seen as ‘true’. Many color-change gems also will show part of the color change in a photograph if the photographer is not careful to filter out extraneous light sources.

So what can you, as a buyer do? If possible, look at the gem in person, rather than in a picture. If that is not possible, know your seller and check out the written description of the color of the gem and see how much it differs from the photo. You can email the seller and ask for a more detailed description of the color. It is important to remember that personal preference is primary if the gem is to be worn and enjoyed. In natural alexandrite, the standard for color is an intense Emerald Green in daylight and a change to rich Purple in incandescent or candle light- the more red tones in it the better.

At the present time, bluish-Green seems to be the most popular daylight color with a change to rich Purple the most popular incandescent coloration.

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More Facts in Perceiving Color in Colored Gemstones

Looking at an email photo of an incredible alexandrite (with an accompanying incredibly high price tag) from one of my agents many years ago, I knew I wanted the alexandrite. Pristine Emerald Green with a slightly bluish undertone that color-changed to an incredible Blood Red with Ruby Flashes. Saturation was perfect. Tone was perfect. Hue was what I had always known the Perfect Alexandrite would be! I anxiously awaited the gem and when the parcel came, I couldn’t bring myself to open it for several hours.

Disappointment, disbelief, and increduality followed my first sighting of this Alexandrite. The colors were too saturated leaving the stone almost black. The color-change was a blackish-Purple. How could this be? Was it the same gem? The answer is YES, it was the same gem and the following information will tell you how it could be that the same gemstone looked so different in Florida from India.

Any purveyor in gems soon learns that ‘all light is not equal’. As discussed above, The color of a colored gemstone can, and does, change according to the light it is seen under. Several factors account for this- the first and foremost is the quality of the light. Ask any gem buyer and they will tell you that light affects the color of a gem. Most buyers prefer to view gems under northern light through a skylight or window (without the direct effect of the sun beating down on the gem).

The AIGS conducted a study of the effect of light on gemstones. They found that not only does the time of day effect the color, but also latitude, quality of the air (smog, pollution), humidity, and weather- all of which will show the same gemstone in a different shade or tone of color.

Morning light has more blue in it and will show blue stones to their best advantage while afternoon light has more yellow and will show red or reddish gemstones to their best advantage. Weather at different latitudes is different with drier air having bluer skies and more humid air having paler skies. Paler skies tend to have weaker strength of light with a corresponding result of paler stones showing as deeper in tone while bright blue skies with accompanying bright light show deeper toned stones to better advantage.

With alexandrite and other color-change gemstones there are two factors at work: daylight or fluorescent light for the green coloration and candlelight or incandescent light for the red or purple coloration. Intense and vivid daylight here in Florida, for example, may show what is a bright and vivid colored gemstone as having too dark a tone in Australia or other southern latitude where air quality is different and sunlight is more muted.

Color-change is even more difficult to assess: different incandescent bulbs have differing amounts of red wavelengths all of which show color-change differently. Some incandescent bulbs have blue wavelengths, which won’t show much of a color-change at all. Humidity will tend to ‘wash out’ a gem’s color, while crisp air will make a color seem to intensify.

What all this amounts to is that even gemstones you now own can appear slightly different in tone, color, and saturation from day to day.