Purkinge Shift, Color, and Gemstones

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 5mm Alexandrite Color Change

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.


Subscribe To Our Friends List

and receive Super Specials and great Discounts via your inbox

please type your Email:



 

Copyright Khazargems © 2005-2017