Color Change/Color Shift

Color change/color shift; whats the diff?

More on Topaz prices:

By Richard W. Wise

© 2007

I Get Emails:

I love hearing from readers. I get numerous emails every week from all over the world mostly from folks have read Secrets Of The Gem Trade. Some of you write asking detailed questions, often already answered in my book, which would require much more time than I have available to answer. Others send images of gems they are considering buying. My apologies but if you want my professional opinion about a purchase, I am going to charge you a professional fee and I don’t work from images.

The forums are an ideal place to ask these sorts of questions: For questions on gems; log onto www.gemologyonline.com. These folks love difficult questions, the more difficult the better. For questions about pearls I recommend: www.pearl-guide.com

Color Change versus Color Shift Gems:

Just the other day, Jan Glover wrote asking a stimulating question.

“First, would you please try to explain the difference between a color shift and a color change gemstone to me? I have seen garnets posted on the internet that change color from a purple to a pink in different types of lighting, is this (pictured above) a color shift garnet?”

Great question Jan!

First a little color theory, consider the color wheel. Actually, there are several color wheels, the one we are interested in is the spectral color wheel, that’s the one that divides white light into its constituent colors or hues. To that wheel we make a couple of additions. The eight chromatic hues present in gemstones are; red, orange yellow, green, blue violet, purple and pink. The first six are the spectral hues, the last two; purple, a hue that lies half way between red and blue and pink (pale red) are known as modified spectral hues. If we were using terminology rigorously as we should, we would not even use the term color. Properly speaking; the terms should be; hue shift and hue change

Gems change color when the lighting environment changes. In the old days there were just two types of light; sunlight and the light from a flame. When alexandrite was first discovered in the Ural Mountains in the 1850s the standards were noon daylight and the flame of a candle. As we passed into the 20^th Century the candle was replaced by the light bulb. This change passed unnoticed and led to some confusion and to the prevailing myth that alexandrite changes color from ruby red to emerald green. At 1500 degrees Kelvin, candlelight is distinctly reddish whereas the light emitted from a standard light bulb at 3200 Kelvin is well into the yellow. Thus, an alexandrite viewed by candlelight will appear to be much redder than that same stone viewed under the light bulb. Fact is the night time color of alexandrite regardless of source has always been purplish-red to reddish purple or as the great German gemologist Max Bauer described it in 1904: “an emerald by day and an amethyst by night.”

In 20-21st Century gemology, the two types of lighting used to judge color change in a gemstone are sunlight, specifically north daylight at noon and incandescent or light from a standard light bulb. North daylight at noon is fairly balanced white light between 5500-6500 Kelvin. Standard incandescent is yellowish light with a Kelvin temperature of 3200. Specificity is crucial; in today's technological world it is possible to dial-a -hue, light sources are available with Kelvin temperatures that cover practically the entire color spectrum. Caveat emptor!!

Many gemstones will exhibit alterations of hue when the lighting environment is changed as specified above. There are three possibilities:

1. Gems that shift part way between two adjacent hues. For example a pink sapphire that shifts from violetish pink to pinkish violet.
2. Gems that shift from one adjacent hue to another. Sapphires that change from purple to blue are a good example.
3. Gems that leap across the color wheel from one (non-adjacent) hue to another. For example, alexandrite and some garnet that change from purple-red (P-R) to blue-green. (B-G).

In my opinion, no. 1 should be called a color shift and cases numbered 2 and 3 should properly be termed color change. The first case is a change in degree not in kind, the hues shift only partially from one hue to another, never completely. In the second and third cases there is a change in kind not just degree. In both 2 and 3 we see a true change of hue. I have seen certain Sri Lankan sapphires change from a slightly grayish blue to a true purple and, of course, there is the example of alexandrite and certain alexandrite like garnets.

As to your question Jan, impossible to say. First question what light source was used in capturing that image? At a guess I would say that we are looking at a rhodolite color change stone. I have found one or two in parcels in East Africa over the years. Given my classification, the stone would fall into category no. 1 and be classified as a color shift garnet.

Recently, there have been quite a number of color change and color shift garnets, some in fairly large sizes, coming out of Madagascar and East Africa. Don’t mistake this for abundance, color changing and color shifting gems are fairly rare. Several years ago I picked though literally thousands of rhodolite garnets to find just three that shifted from pinkish-purple to purplish-pink. Garnets with the alexandrite like color change are even rarer.

More on Topaz Prices:

Somebody mis-spoke, probably me. What I meant to report in my last post was that topaz prices in Brazil had increased dramatically over the past several years. In a recent post on www.yourgemologist.com , New York dealer Steve Lembeck takes issue with the figures reported in this blog. David Epstein agrees with Steve Lembeck. According to Epstein prices at this year's Tucson shows were up between 20-40%; peach up 20%, peachy/pink up 25%, pink up 25%, sherries up 30% and reds up 40%.

Epstein continues to maintain that prices, based on actual transactions in Teofilo Otoni, have increased 200-300% but this increase has been over a period of three and one half years. Hopefully that clears up my confusion, mea culpa!

Interested in reading more about real life adventures in the gem trade? Follow me on gem buying adventures in the exotic entrepots of Burma and East Africa. Visit the gem fields of Austrailia and Brazil. 120 carefully selected photographs showing examples of the highest quality gems to educate the eye, including several of the world's most famous gems. Consider my book: Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones.

“Wise is a renowned author... He’s
done a marvelous job of this first book, monumental work, a tour de force...My recommendation: Buy this book”.

Charles Lewton-Brain, Orchid

Only $39.95. Read a couple of chapters online: www.secretsofthegemtrade.com.

Buy it on Amazon: www.amazon.com

Semiprecious; A Term In Search of an epitaph

In this post: Book Review: Hope Diamond by Richard Kurin

by Richard W. Wise, G.G.

©2007

Semiprecious is like semi-pregnant, it is a word that makes no sense. No less an authority than Robert M. Shipley, the founder of GIA, called it “an indeterminate and misleading classification”. Still, some people, including a good many dealers, stubbornly cling to it like limpets sucking on a rock. In ancient days do you suppose King Tut and the rest of the royals knew that they were using second class gems to decorate their tombs? When will this term finally be consigned to the linguistic dustbin where it truly belongs?

The French philosopher Voltaire insisted that intelligent discussion was impossible unless terms were defined. I contend that the precious versus semiprecious is a distinction without a difference and that semiprecious is a truly meaningless term. To use a meaningless term is to talk nonsense. To prove the point, I will issue this challenge. I say that the term precious cannot be defined in a way that excludes gemstones other than the usual list.

Consider, if you will, the usual suspects: The list of precious gems usually includes: diamond, ruby, blue sapphire and emerald. Right? Well if so what criteria make these gems and only these gems precious? All possess the usual criteria; beauty, rarity, value, durability but to the exclusion of all others? Take beauty, emerald can certainly be beautiful but is it more beautiful than its first cousins the aquamarine, the red beryl, the heliodor? It is worth more in the market than aquamarine and heliodor but is far more abundant and lower priced than red beryl.

Alexandrite, is another case in point, it possesses all of the criteria and is rarer than every gem on the list yet it is excluded. Why is blue sapphire a precious gem and yellow sapphire only semi-precious? Cuprian tourmaline from Paraiba, Brazil is hugely expensive, it is certainly beautiful and rare and durable to boot. Why isn’t cuprian tourmaline considered a precious gemstone?

If its precious, its, well precious but if it’s semiprecious is somehow less than precious. What makes one stone precious and another less so and why, one might ask, would anyone marketing a product use a term to describe that product that denigrates that product?

Win a Free Book:

I will give a free signed, hardbound copy of the 1^st edition of my book: Secrets Of The Gem Trade, The Connoisseur’s Guide To Precious Gemstones to the first of my readers to provide a definition of the term Precious that includes diamond, ruby, sapphire and emerald and excludes all other gemstones.

A couple of ground rules; First, according to The Pocket Oxford to define means to “ to mark out the boundary of…to give the exact meaning of a word” thus if I say andesine is a precious gemstone the question is, what are the criteria that determine preciousness and does the given gem meet them? Second; a definition is not a list so something like “precious is a gemstone category that includes diamond, ruby, sapphire and emerald.” is not acceptable because it is redundant like saying a “a rose is a rose”. What is required and acceptable is a true definition one that provides a basis, a series of criteria by which a stone is either included or excluded from the select company of precious gems. Third: Your answer must be posted in the comments section (below) of this blog post on or before April 20, 2007.

Book Review:

Hope Diamond, The Legendary History Of A Cursed Gem by Richard Kurin, Smithsonian Books, Harper Collins. $24.95

This wonderfully researched and lively account traces the story of the Hope Diamond and in the process debunks and dispels much of the misinformation surrounding the world’s most famous gem.

The debunking begins on page one. Years ago I heard a story that Harry Winston shipped the Hope to the Smithsonian by regular mail in a plain brown paper wrapped package. It went by mail alright in a plain brown wrapper but it was insured for a million dollars.

Kurin begins his tale at the beginning by making his own journey to northwestern India to the fabled Kingdom of Golconda and the storied mines of Kollur. This is the mine mentioned by the famed 17^th Century French gem merchant, Jean-Baptiste Tavernier. Tavernier, the man who sold the diamond to Louis XIV of France was famously silent about where he obtained the stone but he does mention Kollur as a source of colored diamonds and based on that single mention, most experts have deduced that Kollur was the source.

What did he find in Kollur? Snakes! After a difficult three day journey following Tavernier’s route by car, snakes and very little else. There exists barely a trace of the old mines which were played out and abandoned in the 18^th century. The presence of snakes together with a nearby mountain and bit of local folklore leads Kurin to speculate that perhaps, Kollur was the site of the original Valley of the Serpents mentioned by Marco Polo. A bit of a leap, perhaps, unlike Mogok, Kollur isn’t a deep valley but the locals do have a two-headed bird god and that is something the Burmese contender lacks.

Source of The Great Blue:

Kurin pulls together an interesting, if flawed, argument for Kollur as the source of the Hope. He points out that when Tavernier sold the stone to the Sun King, the Hope was barely fashioned, almost rough. From this he concludes that the stone was purchased at the mines.

His next conclusion is a bit more of a reach. With the meticulous attention to detail that he demonstrates throughout, Kurin discovered a short note by Tavernier on the original chart made up by the French gem merchant, describing number six of the best twenty stones Tavernier sold to the French monarch in 1668.

“C’est un autre diamante que j’achetais l’an 1653 a la mine de Coulour.”

Taking this statement and the fact that there are no other stones immediately adjacent to that bit of text, the author speculates that the autre diamond, to which Tavernier refers, may be the blue and if so, Kurin concludes, it was purchased in 1653 at Kollur.

The question is; to which diamond does the note refer and was number six another diamond purchased or another diamond purchased at Kollur? The passage can be read either way. The note, as Kurin points out, was not next to the Hope which was number one on the list. To that I would add two additional points that pose certain difficulties in accepting Kurin’s speculations: First, number six is a colorless diamond and both the stones, numbers five and seven, immediately adjacent to number six are also colorless and second; number six is shown as completely faceted even though, according to Tavernier’s own words, it was originally purchased at the mines at Kollur. Fact is, any dealer worth his salt knows a bit about recutting. The real question is; why if Tavernier did hold on to the stone for fifteen years why didn't he recut it?

To the above I would add a further quibble. Tavernier was a dealer and speaking as a dealer I can state with some authority that our biggest thrill is the hunt. After the adrenalin rush of bagging a big, beautiful and expensive stone, a dealer’s next thrill is selling that big beautiful expensive stone to obtain the capital to begin the hunt all over again. Would a dealer hang onto such a treasure for 15 years if he could have sold it? I doubt it.

Harry Winston and The Smithsonian:

The book is a great read. I discovered interesting facts and important information not previously available with each turn of the page. One particular favorite is the section in which the author reproduces the correspondence between Harry Winston, his lawyers, The Smithsonian, their lawyers and the IRS and its lawyers that detail the labyrinthine negotiations that resulted in Harry Winston’s donation of the Hope Diamond to The Smithsonian. Winston was more than willing to donate the Hope Diamond to the Smithsonian but he was also determined to receive its full value as a tax deduction.

Cartier versus Evalyn Walsh McLean:

In Chapter 19 we learn that Pierre Cartier was the man most responsible for promoting the Hope’s hard luck legend. Cartier bought the Hope in 1910 for $110,000 and was successful in selling the great blue to Evelyn Walsh McLean and her husband for $180,000 the same year. Cartier’s myth making nearly backfired, fearing the curse, the McLean’s tried to back out of the deal and Cartier had to seek court action to enforce the sale. In the end the fabulous wealthy socialites bought the stone on the installment plan for $1,000 a month.

Hope Diamond is the most authoritative account of the legendary blue gem published to date. It is also a great story packed with anecdotes detailing the machinations of the rich and shameless. Highly Recommended. Under 20 bucks on Amazon. Buy on Amazon

Interested in reading more about real life adventures and secrets of the gem trade? Follow me on gem buying adventures in the exotic entrepots of Burma and East Africa. Visit the gem fields of Austrailia and Brazil's famous Capao mine. 120 photographs including some of the world's most famous gems. Consider my book: Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones.

“Wise is a renowned author... He’s
done a marvelous job of this first book, monumental work, a tour de force...My recommendation: Buy this book”.

Charles Lewton-Brain, Orchid

Only $39.95. You can read a couple of chapters online: www.secretsofthegemtrade.com.

Buy it on Amazon: www.amazon.com