The elusive color of yellow green in the oval.#1155

Bright yellow to yellow green oval. This oval finds it easy to slide all around yellow to green. It is very slightly included, which can not be seen face up. It has fine crystal and a medium tone level. It weighs 1.92 carats.

At times I have used the word “dynamic” to discuss color in tourmaline excessively.  But thinking back threw the posts I have written for my site, I have not used the term that much.  Maybe it is because the pictures you see are only a brief moment in the life of color that many tourmaline lead and I don’t want to stretch your credulity for the moments I can not show you.

When I saw “Laurellite” go from purple to blue, others go from blue to green, and others orange to red and others yellow to green and of course back again I wanted to know why.  The why is stronger because many of the same colors do not slide or change much with different “white” light sources.  Even in the broadest most generalized definition of color change in gemstones there is not agreement.  Laurellite can not have its reverse alexandrite color change effect, a warm color(purple)in a cool light source and a cool color (blue)in a warm light source and have the conventional theory of color change in gemstones be true, period.  Yet the endless reciting of the example of ruby, alexandrite and ruby is presented as the clear validation of a nearly universally accepted theory of color change that is based solely on the distribution of different wavelength in the spectrum of the light with complete disregard for the adaptive nature of man’s vision.

I purchased my spectrometer, which is presently (2013) being upgraded and repaired, to go on a great adventure.  The first phase of that adventure was to discover which gemstones in my collection contained copper as a chromophore and that has been pretty successful.  Now I want to try and more fully understand the dynamic nature of the color of tourmaline.  Not in the broadest terms like I supported with Laurellite, but the specifics of tourmaline that you might see and even buy someday.  Why haven’t the gemological laboratories of the world not done more with tourmaline?  Because there has been very little economic incentive, which may be changing because of Paraiba.  And frankly how many $100 gemstones are the GIA going to test for a much greater fee unless that gemstone is pretending to be something much more expensive?

Every digression needs a starting point and so we return.  The posted stone made me stop posting last night because it had yellow on the storage box and all I could see was a very greenish yellow.  In the morning light I see yellow with more or less green.  So I looked threw my collection and found a larger shield cut (#1124) which said yellow green on its storage box, that matched the oval I am investigating, by my eye, under my yellowish light.  So I was ready for the acid test which is comparing the two gemstones under the gray morning light.  Well the shield cut went greener and the oval went yellower, how about that!  So I am to the point where I don’t even trust my eyes.  My spectrometer should illuminate these gemstone’s differences without my eye’s assistance.  Data will follow as soon as possible.

On the gemological note, the bright oval is very slightly included, which can not be seen face up.  It has a medium tone level and fine crystal.  It slides home at a nice 1.92 carats and is embarrassed by the all the attention.

Bruce

 

About Bruce Fry

I was born in Summit, NJ in 1947 and graduated from Summit High School in 1966. I graduated from the Colorado School of Mines in 1970 and after spending another year in graduate school, I left to see the world of Brazil. After spending some more time discovering myself, I ended up working for the Commonwealth of Pennsylvania for 32 years as an Air Quality Engineer in the Department of Environmental Protection. I retired in 2007 and took up faceting gemstones again after a long hiatus that reached back to my twenties. I had started cutting cabochons when I was 13 and bought my first faceting machine when I was 15, but ran out of money and time until I retired.
My great love in gemology is tourmaline and the collection presented here represents my effort to get as much beauty and variety in the colors of tourmaline as I can. I was particularly lucky in being able to get unheated cuprian tourmaline before copper was discovered in gem grade tourmaline from Mozambique.

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