Gota de Aceite: an important drop in the sea of emeralds’ beauty or Fifty shades of green.

«… For me, emerald is the exemplification of mystery, charm and beauty in
the realm of stones. It is a royal stone, a symbol of kingliness and power ... 
In whatever language you pronounce the name, it sounds like music…. 
Esmeralda in Spanish, ?meraude in French, smaragd in German, 
Zummarud in Arabic – all are variations on the same fascinating subject»
 
“EMERALDS, A Passionate Guide” Ronald Ringsrud
(translation from Russian ) 

“The book is about love…The present edition aims at explaining the reader the miracle of silent contemplation of the beautiful stone. The moment when at the sight of the stone’s natural beauty your mind is carried away to such a distance, where gemology science becomes meaningless. We surely study gemology to reach the point, but when we reach it, we call for the help of philosophy, poetry and aesthetics to realize the moment of truth: the moment of connoisseur”

“The book does not merely introduce emeralds to you; it rather gives you a basic idea of the truly royal vision, through the prism of which experts investigate color, clarity and quality of a gem. The new perspective reveals you a secret of bringing into your life a new rare beauty, incarnated in magnificent emeralds and people who love them”. - Ronald Ringsrud. “EMERALDS, A Passionate Guide”.

Such boundless and amazing world. Not just because my work began on the vast expanses of the Internet. Not only because it gave me the opportunity to meet wonderful and talented people. Just because I met people who seem to feel the way I do ...Possibly, I would not ever had any idea of the book if it had not been for Vincent Guy Raffin (bygats), who is on the other side of the world, in Hong Kong, who quoted a few lines from it. Several days have passed and I am reading it…..I am opening it, looking through it…It is amazing for me how excitingly it is written, with the soul of a poet and academic knowledge. It appears impossible to get a better description of emeralds, people, beauty and love than we can get from Ronald Ringsrud’s book “EMERALDS, A Passionate Guide”. You can find the full version of the book here.

And we would like to bring to your attention a few extracts from the book, which refer to the rarest and most valuable quality of the emerald, not known to general public- Gota de Aceite.

«There is no better place to rediscover wonder than in a remarkable phenomenon that occurs inside the finest emeralds. That phenomenon is called gota de aceite (Spanish for “drop of oil,” pronounced “go-tuh day ah-say-tay”). A velvety interruption of the light passing through the emerald, the effect is prized by connoisseurs in the same way they value the velvety texture of a Kashmir sapphire. In both cases, the color of the stone is softened and the internal reflections are spread by numerous microscopic inclusions, reducing extinction and giving a liquid, velvety texture. Gota de aceite is associated with the Colombian emerald, and even in Colombian stones it is visible in only one in a thousand, mainly of fine quality. In six years of informal study of this phenomenon, I have only detected it rarely, personally viewing about 18 good examples, 20 moderate examples and 50 that were muted or indistinct.

The term gota de aceite is also known as the “butterfly wing effect” (efecto aleta de mariposa). Transparent irregularities in the internal crystal seem to be the result of changing and unstable conditions during emerald crystallization. These conditions give rise to both raised hexagonal terminations as well as etched geometric depressions. After their formation, these growth structures are overgrown with more emerald. The growth structure and patterns thus formed are transparent and diffuse the light within the faceted emerald in a manner reminiscent of a drop of thick oil, hence the name.

Angular growth structures, photographed at 30x magnification, are typical of the gota de aceite phenomenon.

Since growth structures cause the effect, there is no reason that it could not be found in emeralds from localities outside of Colombia.

This phenomenon was also referred to as calcite precipitation. It was thought to be caused by a temporary lull in the crystallization process of the emerald, allowing small grains of calcite to form that were later overgrown with emerald. The calcite theory is losing out to another explanation of gota de aceite. Close microscopic examination indicates the presence of growth structures instead of calcite, according to researcher John Koivula. He points out that the forms appear three-dimensional when viewed perpendicular to the plane of their formation, but when the stone is turned sideways, there is no space for them; they look flat. Also, no evidence of calcite was seen, either by microscopic examination or Raman spectroscopy.

The growth structures that cause gota de aceite can be somewhat difficult to see. The photo on the left reveals the angular or hexagonal growth features seen when looking down the c-axis. On the right, the same emerald is shown perpendicular to the c-axis, which reveals the typically narrow bands of columnar structures associated with this phenomenon.

In the gota de aceite effect, the etching and regrowth structures form in a plane perpendicular to the c-axis. If the emerald cutter positions this plane roughly parallel to the table of the faceted stone, it will be seen and appreciated by the viewer, increasing the emerald’s value and allure. Sadly, the effect gets wasted when the emerald’s owners and cutters do not recognize the effect and position the zone of gota de aceite to one side or perpendicular to the stone’s table. The difficulty of seeing it in the rough, along with the lack of understanding about it, are other reasons for the great rarity of gota de aceite emeralds in the market.

Sometimes the gota de aceite effect can only be found by first looking through the pavilion, especially if it is a muted example. In the case of this 3.65 ct. emerald, the effect was visible through the table. Turning the emerald under magnification and varied lighting will reveal its extent.

Only among connoisseurs is this phenomenon understood. In Colombia, only experienced dealers recognize the butterfly wing effect; others overlook it. Nowadays, in Europe and the United States, the expression gota de aceite is often used to describe any fine emerald, even if it does not have this effect. Also, the expression “drop of oil” has fallen from use because of the negative connotation of the word “oil” in the last two decades. Yet the term has been used by at least three generations of Colombian emerald dealers.

The 2.77-carat emerald pictured below is a wonderful example of this phenomenon. It was highly prized and sold to a collector for $8,000 per carat nine years ago. In this face-up view, the softening is especially visible through the table, where there is internal reflection of the pavilion facets.

A 2.77 carat emerald with the “butterfly wing” effect. The view of blurred facet edges through the pavilion facets is the first indication of gota de aceite. Viewing the emerald in the hand and rocking the stone slightly will bring out the liquid softening effect.

Confusion of nomenclature with regard to gota de aceite has taken two forms. Because the phrase is typically used only with respect to very fine emeralds, some exceptional stones are labeled with this term even though they do not actually have the effect. The mere fact that the emerald is very fine often inspires the owner or seller of the stone to use gota de aceite as a superlative.

There is also confusion relating to “old mine” emeralds. Old mine is a separate term attributed to rare and fine emeralds, but it refers to the provenance and age of the emerald, specifically those emeralds sent by the Spanish colonies in the New World to Europe and Asia in the sixteenth through eighteenth centuries, along with Swat Valley and Habachtal emeralds of the same era. However, the presence of gota de aceite may wrongly inspire the owner or seller to call the stone “old mine.”

Graff Diamonds ring with ”Old Mine” Colombian Emerald of 8.88 carats

In addition to the butterfly wing effect, Colombian emeralds are blessed with a natural fluorescence that takes in visible light and sends it back to you as a red message of passion underneath the sober and respectable green color. The red is invisible, but it subconsciously grabs your attention: rather like the way a woman who may be dressed in a normal manner is found wearing perfume of the most primal and powerful scent. The man didn’t see anything, but whatever it was, he now finds this person irresistible. The butterfly wing effect is like adding romantic music to the above scene of enchantment and allure. Can anyone resist?

Now that we are in the depths of colored stones enchantment, this is a good time to refer back to the writing of passionate ruby expert Richard Hughes. The reason that ruby from Burma (now Myanmar) and emerald from Colombia are at the absolute top of colored stone desirability and price is that they both share properties like the ones mentioned above in remarkably similar manners. Colombian emeralds have not only fine color but natural fluorescence and microscopic inclusions whose presence reduces extinction. The Burmese ruby fluoresces too, and has inclusions, called silk, that spread the areas of color without reducing transparency. Hughes explains the phenomenon:

“What gods are these? Not only did they bless the ruby with an inborn glow to match its scarlet skin, but such was their benevolence that they also gave us silk – oriented needles of rutile – gossamer threads that banish the darkness besmirching the rest of the mortal gem world.

Such tiny exsolved inclusions scatter light onto facets that would otherwise be extinct (dark). This gives softness, as well as spreading it across a greater part of the gem's face.”

“…There is something in emeralds that adorns even the sheets of paper on which the word is written" - Luis Kornitzer, English trader in gems and an expert of pearls, from “The jeweled trail”, issued in 1955.

 

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Tatyana Pfaifer

The founder of Jewellery Masterpiece