Book Review: American Cut, The First 100 Years by Al Gilbertson

by Richard W. Wise
©2007

Al Gilbertson, G.G.
The Gemological Institute of America
Paperback, 214 Pages. $29.95

American Cut, The First 100 Years, sets the record straight. Al Gilbertson tells the true story of the development of the ideal cut round brilliant diamond. First, Gilbertson clears away the prevailing myth endlessly repeated by industry writers, including this one, that Marcel Tolkowsky was the first to articulate the proper proportions for fashioning a round brilliant cut diamond.

Gilbertson has done his homework. He traces the origin of a finely cut diamond from its origins in Early European history to a maverick American jeweler by the name of Henry Morse. Morse, a jeweler not a cutter, opened a diamond cutting shop in Boston around 1860. Morse had the idea that improving the cut of a diamond would result in a more beautiful stone and that better looking stones would sell better. This revolutionary concept brought him in direct conflict with his own employees, diamond cutters educated in Europe where cutters were actually fined if they lost too much weight cutting a diamond.

The author makes the point, not unknown to young men shopping for an engagement ring today, that in diamonds, better meant bigger. From earliest times, European monarchs were in competition with one another to own the biggest diamonds. The ownership of a big rock was a status symbol that added luster to a reign not to mention being a highly portable source of ready money. Not everyone agreed, Louis XIV, the biggest gem collector of them all, ordered his jeweler, Pitau to recut the French Blue from a hefty 114 carats to a mere 66, a loss of 41%, simply to improve its sparkle.

Morse has the good luck to hire a fellow named Charles Field, as his shop foreman. Field invented a mechanical diamond bruting machine that replaced the old method of hand rounding, a laborious process of hand rubbing that required weeks to shape a single gem. Morse experimented with a series of cutting angles and by 1870 had discovered crown and pavilion angles that dramatically improved face-up appearance. Morse and Field then invented a gauge to be used by their cutters to achieve the true precursor of modern "ideal cut" round.

There is a whole lot more. Gilbertson takes us right to the present discussing the influence of Tolkowsky and American pioneer gemologists, Frank Wade and GIA founder Robert Shipley. Gilbertson’s own insights into beauty and diamond cutting are of real interest. He was part of the team that researched over 70,000 sets of proportions that led to the new GIA diamond cut evaluation system and knows whereof he speaks.

Profusely illustrated, well researched and thoughtfully written, American Cut, The First 100 Years gives us the real story. It is one of those books that deserve a place of every gemologist’s library. At $29.95 it is a bargain. Order here

Ordered American Cut, The First 100 Years? Still have a few dollars left?

Follow me on gem buying adventures in the pearl farms of Tahiti. Visit the gem fields of Australia and Brazil. 120 carefully selected photographs showing examples of the highest quality gems to educate the eye, including the Rockefeller Sapphire and many more 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

whether you like to know what the best colour is in Tanzanite, or how to grade a Diamond, you will find it in this book. No other book I read before dealt with this topic is such detail as Richard Wise's masterpiece."

A. Van Acker, FGA
Amazon June 2005

"Secrets Of The Gem Trade: The Connoisseurs Guide To Precious Gemstones by Richard W. Wise is an impressive new reference for dedicated dealers and collectors of gems, gemstones, and ... pearls. Introducing and descriptively exploring each and every gem covered in the easy-to-use reference, Secrets Of The Gem Trade contains an illustrated summary of each stone inclusive of its history and general information, hue and tone, saturation, which may be noticed as the finest, an understanding of the particular gems rarity, and the caution for synthetics and how to depict them, however depending upon the stone there may be description of clarity, color fading, multi-color effect, etc. Secrets Of The Gem Trade is very highly recommended to anyone interested in gemology as a superbly organized, authoritative, comprehensive, and easy-to-follow reference."

Midwest Book Review
April 2006

Only $37.95. Read a couple of chapters online: www.secretsofthegemtrade.com.

Buy it on Amazon: www.amazon.com

Golconda Diamonds Part II

Golconda: The Legendary True Blue White Diamond--The Rarest of Them All

by Richard W. Wise
© 2007


Just recently it was my good fortune to examine one of the legendary diamonds of Golconda. These gems were originally mined in India in the 16th-18th Centuries. The mines were tapped out by about 1725. Many of the world's most famous diamonds, including the Regent and the Sancy (pictured above right), The Hope and the Koh-i-Noor came from the mines of Golconda. This gem was accompanied by a GIA certificate rating it D Flawless, the highest possible diamond grade and a Gublin Laboratory certificate that identified the stone as a Type IIa. (Regent above left, Sancy above right)

As discussed in my previous post, recent scientific analysis has shown that diamonds with proven Golconda provenance are of a specific type of rare, pure carbon diamond known as Type IIa. Less than 1% of the world's diamonds are Type IIa. Scientifically speaking, Type IIa diamonds are an almost pure carbon diamond containing no significant amount of nitrogen in the crystal lattice. Nitrogen is the impurity in diamond that imparts the yellowish hue. The lack of yellow makes for a pure colorless (D,E,F) color diamond. Some experts claim that all Golconda diamonds are Type II. There is, as far as I know, no scientific evidence to back up that claim.

Blue-White Beauty:

Golconda stones are the true blue white diamonds of legend. Today, dealers use the term blue white to describe diamonds that exhibit blue ultraviolet fluorescence. About 30% off all diamonds will exhibit this characteristic. Though ultra-violet fluorescence is not visible to the naked eye, though its effect may be. Blue is the complement of yellow, meaning that blue fluorescence in diamond effectively cancels out some of the yellow in the diamond's body color. As a result, fluorescent diamonds will face up whiter than their actual color grade might suggest--a fluorescent H might look like a D color. It is UV fluorescence is also responsible for the super-charged saturation of very fine Burma-type rubies.

The gem I examined, a 9+ carat D-Flawless took on a distinct distinct bluish glow in direct sunlight. I had never seen this before. The blue glow was distinct and visible. Unable to believe my eyes I re-examined the certificate, it read: "no fluorescence"! I checked the stone myself, there was absolutely no fluorescence in either short or long-wave UV. How could this be?

Ian Balfour in his book, Famous Diamonds specifically mentions a "light blue tinge" as a characteristic of The 140 carat Regent Diamond. The Regent, originally called "The Pitt" was brought to England in 1670 and is, unquestionably, of Golconda origin (above left). Diamond scholar Herbert Tillander describes this affect as a "blue afterglow." and notes that most Type II diamonds do not fluoresce. One exception, the Hope Diamond, a Type IIb (contains Boron) will not only fluoresce it will actually phosphoresce meaning that the stone will continue to glow last after the UV light source has been removed. Tillander further notes that some Type II diamonds have been found in South Africa's Premier Mine, other sources mention Brazil.

Blue Haze:

Not all Type IIa diamonds exhibit this characteristic though Golconda stones do. I was able to examine another D-Flawless type IIa that placed side by side with the 9 carat, failed to exhibit the blue glow. In the Golconda stone, in direct sunlight, the blue hue floated above the gem like an early morning haze.

Fine Crystal; The 4th C:

Perhaps due to their pure carbon composition, Golconda diamonds exhibit another characteristic, a high degree of transparency, Balfour describes The Regent as having a "unique limpidity" that some dealers refer to as "super-d" or what I refer to in my book Secrets Of The Gem Trade, as a super-crystal. Very fine gems of all colors possess this characteristic. Compare a regular wine glass with one made of lead crystal, hold both up to the light and you will get the idea. When compared to another D color Type IIa not of Golconda origin, the difference was unmistakable. The characteristic strikes one as a combination of ultra-limpidity coupled with what connoisseurs refer to as "whiter than white" both characteristics were visible in the Golconda but not in the other gem.

The stone I examined was cut in a fashion almost identical to the Regent, a cut known as a baroque brilliant or old European (image left). Stones cut in this fashion are of a different character than the modern brilliant. The crown is higher and the pavilion facets are shorter and broader.

A fine diamond possesses two characteristics that define its beauty, brilliance and dispersion. Dispersion is the ability to break white light up into its constituent rainbow colors. In the single minded pursuit of maximum light return, modern brilliant cut gems have sacrificed dispersion to produce maximum brilliance. As a result they have become soul-less light return machines. A well cut baroque brilliant by contrast will exhibit a balance of brilliance and dispersion that gives the diamond its distinct character and beauty--a character that is missing in so many modern super-ideal cuts.

(image above, side view of Golconda diamond), Compare the color of the center with the side trillion that is definitely not of Golconda origin.

To summarize, there appear to be three visual characteristics that define the beauty of Golconda diamonds: A high degree of limpidity (crystal), an ultra-whiteness and a blue afterglow that appears in natural daylight. Golconda gems are Type IIa diamonds and this can be established by scientific testing. All Type IIa diamonds, however, are not Golconda diamonds; to be considered Golconda, they must possess the visual characteristics just described.

It is unclear whether Type IIa diamonds from other sources possess the characteristics discussed above, there certainly are some that do not. However, in the final analysis, we are interested in gems not geography. in gems beauty is the ultimate criterion. When it comes to Golconda diamonds if they deliver the goods, how much does source really matter.

If you are interested in learning more about Golconda Diamonds or are simply looking for a new way to dazzle your friends at cocktail parties. Read more about the four Cs of connoisseurship. Follow me on gem buying adventures in the pearl farms of Tahiti. Visit the gem fields of Australia and Brazil. 120 carefully selected photographs showing examples of the highest quality gems to educate the eye, including the Rockefeller Sapphire and many more 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 $37.95. Read a couple of chapters online: www.secretsofthegemtrade.com.

Buy it on Amazon: www.amazon.com

“Secrets of the Gem Trade” subject of Ventfort Hall lecture

- July 30, 2007

Described by Gemkey Magazine as “one of the world’s foremost gem connoisseurs,” gemologist Richard W. Wise will bring his expertise to a Ventfort Hall Mansion and Gilded Age Museum visual presentation on Wednesday, August 29 at 4 p.m. A Victorian Tea will follow this final lecture of Ventfort Hall’s summer series.

Admission for the lecture and tea is $15 per person, members $12. For more information or reservations, please call 413-637-3206. Ventfort Hall is located at 104 Walker Street in Lenox.

Lighting and Grading Gemstones Part II

LIGHT UP YOUR LIFE

by Richard W. Wise, G.G.
© 2006

What is the best lighting environment to view gemstones? In part I of this post I discussed the various lighting options and the pros and cons of each. In part II I will write about the lighting some of the world’s foremost gem experts and connoisseurs choose to both view and evaluate gemstones.

Among the experts opinions differ somewhat as to which “daylight” Kelvin temperature is best but each accepts daylight as the standard. Stephen Hofer one of the world’s most respected authorities on colored diamonds, maintains that 5500K works best for colored stones and 6500K is best for diamonds both white and colored. In his lab, which is dedicated to the evaluation of fancy color diamonds, all grading work is done under 6500 Kelvin fluorescents. C. R. Beesley, President of American Gem Labs in New York, prefers Vitalite a bulb manufactured by The Duro-Test Corporation with a Kelvin rating of 5500. "Most people don't do their homework", says Beesley, "comparing color temperature isn't enough..." Beesley tested more than twenty different light sources in the process of developing his Colorscan colored stone grading system to gauge their actual effect on gemstones.

In 1994 GIA completely revamped its color grading system for colored diamonds, shifting from Veralux, a so-called low UV lamp rated at 6200K, (see Secrets Of The Gem Trade, p.60, fn) which remains its standard for grading colorless diamonds to a 6500K average daylight fluorescent bulb for grading colored diamonds. The lamp is manufactured by Kollmorgen Corporation. GIA also uses a 6500K for general research purposes. The Institutes use of light of this Kelvin temperature is in no way an endorsement of the use of this type of lighting by jewelers. According to James Shigley, GIA's Director of Research, 6500 was chosen because it is a recognized standard used by color scientists. Little or no thought was given to enhancing the beauty of gemstones.

Incandescent and quartz halogen lamps can be made to resemble daylight with the addition of a blue filter. Duro-Test currently markets a "super-white halogen" that does the same job. I conducted a series of experiments with the Duro-Test product and found that this type of lighting does wonderful things for blue sapphire, aquamarine and amethyst, but does nothing to reduce the muddy look in blue and green tourmaline. "Super-white" induces a distinctly overblue look in rubies and tanzanite takes on an odd blue/violet multi-color effect quite dissimilar to its appearance in any other lighting environment. In diamond, "super-white" overly enhances the yellow/blue luster of the stone.

The problem!, filtered light makes for unintended results. Unfiltered fluorescent lighting can exhibit a relatively balanced spectrum when graphed on what scientists call a "Relative spectral power distribution" curve. Filtered lamps show spikes in this curve which are areas of color deficiency.

Another type of lighting called Neodymium is currently being marketed as a "full spectrum incandescent". According to Roger Schoenfeld, a lighting specialist with Durotest, this is really a standard yellowish incandescent incased in a special glass invented in Sweden, which reduces yellow and generates a spectrum richer in red and blue. Neodymium is not a bad choice. It is excellent for diamonds. Neodymium is a bit better than standard quartz for sapphire and aquamarine though not as good as "super-white". All three sources suppress the violetish to purplish secondary hue of the finer grades of sapphire.

Compared to daylight, neodymium works well with ruby, amethyst, emerald and tsavorite garnet. It is no worse with blue and green tourmaline which seems to be a true day stone, i.e. it looks its best in daylight and in daylight fluorescent 5000-6000K. Pink & red tourmalines do fine in Neodymium "full spectrum”, it does not produce the brownish secondary hue that most pinks exhibit in standard incandescent but, rather makes them look violetish. Tanzanite looks about the same as with quartz light; bluer than standard incandescent and without the otherworldly quality of "super-white".

Three or four years ago, Tailored Lighting introduced a 4700 Kelvin MR-16 lamp which has the highest Kelvin temperature of any incandescent bulb and may be the best solution yet for interior lighting. The new Solux lamp uses a new type of reflector to boost the quartz halogen lamp into the daylight range. This technology produces lighting with a fairly even power distribution curve (CRI) that shows no spikes in either the red or blue areas of the visible spectrum.

In a short, down and dirty test, Solux worked well with tourmaline, reducing the muddiness produced by all other incandescent light sources. Sapphire and ruby also benefited from this type of lamp, showing they’re colors in true daylight fashion. Solux also improved the diaphaneity of tanzanite. On the down side, Solux appeared to add a gray component to aquamarine and pink topaz which reduced the saturation and flattened the color.

Changing lighting environments have always been a problem for both buyers and sellers. You buy in one light, sell in another. Traditionally dealers who do extensive buying outside their offices have relied upon comparison stones, stones of well known color, which they carry or wear on buying trips.

I use two fixtures with twin four foot fluorescent lamps to give an overall daylight environment combined with several of the new Solux MR-16 4800K quartz halogen lamps in my own laboratory which doubles as a salesroom and consider this combination to be the closest possible to a true daylight environment. I use Duro-Test Vitalite in one fixture and Kollmorgen 6500K average daylight in the other. The use of the 6500K is to compensate for the 4800K Solux, to kick up the Kelvin temperature of the overall environment towards 5500K.

The combination of of daylight fluorescent with Solux works acceptably across the spectrum of gemstone colors. The fluorescents create an overall daylight environment and the Solux MR-16 provides the punch. This lighting temperature gives a balanced daylight color rendering when compared to New England north daylight. Several years ago, a German firm, System Eikhorst, introduced a lighting system based, in part, upon my recommendations. It includes both daylight fluorescent and Solux fixtures.

When making a purchasing decision it is important to identify the light source you are viewing the stone and to view the stone in as many lighting environments as can be found. Regardless of my geographic location at the time, I always compare each stone in daylight and 3200K incandescent to see how the stone reacts at both ends of the lighting spectrum.

If a consistent workable colored stone evaluation system is ever created, the lighting environment will of necessity be standardized. To achieve reproducible results, there are three variables; the observer, the gem observed and the lighting environment. The standardization of the lighting environment will remove one variable. This leaves one remaining variable, the observer. Either we must accept some nuances of subjectivity or build a gem grading robot replace to connoisseur’s eye and dictate our taste.

Light Up Your Life; Lighting and Grading Gemstones, Part I

LIGHT UP YOUR LIFE

Lighting and Grading Gemstones Part I

©2006

Richard W. Wise, G.G.

It used to be so simple, the brighter the light the better the light. You had the light from a fire and the light from the sun, that was it. In those good old days it was easy to figure out watt was watt! Today we have a myriad of options, “warm light”, “cool light”, “daylight.” Gem dealers are beginning to discover that the lights that make his rubies look like a pigeon's blood may make his tourmaline look like a dog's poop. As for the buyer, caveat emptor baby, check the bulb!

We are all familiar with the daylight standard: diamonds and colored gemstones are supposed to be judged in north daylight. Why?, because north daylight, specifically north daylight at noon is white light balanced between the red and blue spectrum. Sounds simple, but wait a moment! Dealers have long realized that the quality of daylight differs in locations throughout the world. North daylight at noon in Bangkok is qualitatively different from north daylight in New York.

The quality of natural daylight is affected by several factors, including latitude and air quality. In addition, the relative strength and color composition of daylight changes as the day progresses. "Don't buy blue sapphire after 2:00pm". That was the advice my Bangkok broker gave me on my first trip to Thailand. This dealer's truism teaches a basic fact that as the day progresses the color composition of sunlight moves from yellowish into the blue range then toward red at sundown.

Color scientists measure color as a function of light temperature and express it in units called Kelvin (K). a light filament heated red will have a Kelvin temperature of 1000-1500K, orange like a candle flame has a color temperature of 1500-2500K, yellow between 2500-4000K, white as in daylight is defined as a range; 4000-10,000K. In practice, increasing Kelvin temperature reduces yellow and adds blue.

If we wish to get a true color rendering using the daylight standard we will want a bulb that produces average noon sunlight with its relatively balanced color spectrum with a color temperature between 5500-6500 Kelvin. Unfortunately, the Kelvin temperature of an incandescent lamp falls between 3000-3200. The new low-volt quartz halogens have a color temperature of only about 3200K. Light in this temperature range is distinctly yellowish and will enhance the look of stones in the yellow, orange and red range. It will add an attractive bluish hue to chromium-vanadium colored gemstones like emerald, chrome tourmaline and tsavorite garnet. However, some Emerald, particularly Zambian emerald, can look distinctly overblue in this type lighting and 3000k light tends to muddy the crystal (reduce the transparency) of iron colored green and blue stones such as tourmaline and sapphire.

Daylight equivalent lighting does exist in fluorescents but not in incandescent single point spot and flood lighting that is used by most dealers and jewelers to bring out the brilliance of a gemstone. Daylight fluorescent bulbs with Kelvin temperatures between 5500-6500 are available. These lamps are marketed, usually as “daylight” lighting by several companies under various trade names. Unfortunately fluorescent lamps generate a diffused light and produce insufficient punch, what scientists call lumens, to bring out the best sparkle in your gems. To further complicate matters, there is no recognized international standard for a daylight bulb. Each manufacturer decides for himself what to consider “daylight”.

Coming next: Part Two, Learn what types of lighting the experts favor, Stay tuned...

So, you want to learn more about lighting and judging gemstones? Read the book:

"Secrets Of The Gem Trade is very highly recommended to anyone interested in gemology as a superbly organized, authoritative, comprehensive, and easy-to-follow reference."
Midwest Book Review
April 2006

www.secretsofthegemtrade.com