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Meet Guy Borenstein: Stuller’s New Senior Gemologist

Guy Borenstein

Guy Borenstein has an easy manner and a quick, warm smile. Yet asked a question about diamonds and gemstones, he’s laser-focused. He speaks with careful, precise phrasing and his intense expression communicates his passion for this subject. I find this more remarkable because he had lived his life in Israel, and English isn’t his first language.

guy borenstein

Initially, I thought he had come to direct Stuller Gemological Lab™, our in-house diamond screening lab, and a significant undertaking. It’s definitely one of his priorities. But he arrived with years of knowledge and experience in various gemological disciplines and now serves as Stuller’s Senior Gemologist and leading gemological authority. His job gives him the latitude to take a holistic approach to many aspects of our diamond and gemstone and other gem-related departments. And as his career will show, he has plenty of experience as a multi-tasker.

I asked Stanley Zale, Stuller’s Vice President of Diamonds and Gemstones, for his thoughts. “Guy is a world-class talent, highly respected among leading gemologists, and we are fortunate to have him join the Stuller team,” he says. “His knowledge and skills will help us continue to lead the industry with robust programs that best ensure the integrity of our products.” If you know Stanley, you realize this is high praise, indeed.

I sat down with Guy to learn more about his journey in the diamond and gemstone world.

ER: How did you develop an interest in diamonds and gemstones? Was there a family connection?

Guy: Actually, no family connection. I was born and raised in Haifa and started collecting beautiful and unusual rocks when I was 10. We were living on Mount Carmel, so I looked there and brought my finds home to explore, and maybe even identify. With each discovery, my fascination grew. I wanted to learn more and more, and it grew into a passion.

ER: You have a curious mind. Where did it take you?

Guy: Yes, you are right about my curiosity. I want to learn everything I can about diamonds and gemstones and any subject that interests me. Each piece of knowledge makes me ask new questions. Where did it take me? When I finished high school, I went to the European Gemological Center school in the Diamond Exchange in Ramat Gan, near Tel Aviv. While attending school, they offered me a two-year internship in their lab. After completing my EGG (European Graduate Gemologist) and working at the lab for 6 months, I wanted to take the next step. People whose judgment I trust recommended I get the Gemmology Diploma (also known as FGA) from the Gemological Association of Great Britain (Gem-A).

ER: Were you able to complete it while still interning in the EGC lab?

Guy: Yes, and during my work there, I started to work also for Gemewizard, where I served as Vice President of Gemological Services. Several years later, I led the establishment of Gemewizard’s laboratory — GWLab —, and was their chief gemologist there and at the EGC lab. During that time, I also started to work for Gem-A as an online tutor for their Gemmology Diploma students.

ER: So you had four jobs at the same time?

Guy: Yes. But they worked together — synchronized — and contributed to each other in many ways. Still, I was very busy. I am passionate about my work, and that makes a big difference. I was enjoying the work and learning all the time.

ER: Weren’t you involved in the development of some Gemewizard applications?

Guy: Yes. I spent 12 years at Gemewizard, and during this time, we developed several solutions for the gemological academy and the gem trade. This was an important tool because the industry struggled to find an accurate way to communicate gemstone color through digital media. It’s critical for grading and online selling of gems so introducing this tool made a difference for everyone.

ER: Was it a way to standardize color description? It seems if everyone used it, this would work effectively.

Guy: That was the main idea. It would be like everyone speaking a common language about color and understanding each other the first time. Later, it was evolved into color-based price list and fully operated gem lab.

ER: You’re reminding me of Pantone® color formula fans that show every possible shade of each color.

Guy: Yes, but the difference is you start with a gemstone and identify its color components, including secondary colors and overtones. And as the gem slightly moves in your hand, this color changes. You cannot just point on one Red-Green-Blue code in a matrix and say that this is your gem color. It’s simply impossible.

ER: That sounds challenging because each gemstone can have multiple shades within it.

Guy: That’s true. Where a gem moves, its physical properties, and the way it interplays with light, we don’t have one fixed color for a gemstone. Gradations may be subtle, but they make a difference.

ER: Tell me more about your time as the chief gemologist at GWLAB and the EGC lab.

Guy: My role was to manage and supervise the advanced testing departments, including diamond screening (for lab-grown origin), colored diamonds grading and testing, and colored stones identification. Besides supervising the lab team and performing various tests, I wrote several research papers and traveled the world presenting at conferences. These interactions with colleagues are very important. I shared my findings, got useful feedback, and learned about many new developments from others. I hope to continue some of that here, but this is not my main role. Now, when I am here, I want to work to offer Stuller customers new services we couldn’t offer before.

ER: Can you talk about that?

Guy: Not yet, but we have several exciting ideas, and they offer great promise.

ER: I’m looking forward to learning more. Be sure to let me know when we’re ready, and we’ll do another interview.

Guy: I will. I’m excited to join Stuller. It’s a worldwide leader in the jewelry industry. And I look forward to building deep relationships with Stuller’s vendors and customers.

As our conversation ends, I think back to the 10-year-old boy looking for stones on the slopes of Mt Carmel. His passion and sense of mission have taken him around the world, and we’re very fortunate to have him here.




Sell With a Story: Black Rose-Cut Diamonds

SWAS Black Rose Cut Diamonds

Black diamonds are back in fashion. So are rose-cut stones. And when you put them together, you have a distinctive combination that lends itself to custom designs. Black rose-cut diamonds offer customers a look that stands out from the crowd as sophisticated, personal, and elegant.  I’m all about big and sparkly, but not every customer feels that way. Many prefer a subtler, understated look that intrigues the eye. Also, women who lead active lives appreciate a rose-cut’s low profile.  

What’s Old is New

Over the last twenty years, millennials and Gen Zs have increasingly embraced vintage looks, and along with this, vintage-inspired jewelry styles have enjoyed a renaissance. These designs feature delicate beading, milgrain, filigree accents, and more. It wasn’t long before customers wanted to make their looks more authentic with distinctive rose-cut diamonds. And black diamonds? Absolutely.  

Unfolding Petals

The rose-cut originated in India around 1520. Later that century, when the rose-cut reached Venice — already a gemstone cutting hub — the city’s stone cutters used newly developed tools to refine its faceting. It reached its peak of popularity during the Georgian and Victorian eras (roughly 1754 to 1900). Round rose-cut diamonds have 24 triangular facets that suggest an unfolding rose, which explains its name. The stone has a faceted, domed top and a flat or slightly rounded bottom.

Ultra-Chic

Remember the “little black dress” — a woman’s go-to favorite for business and celebrations? A rose-cut black diamond ring, pendant, earrings, or all three, carries the same panache. They make fabulous studs or drop earrings, suit many different ring styles, and add allure when set in a pendant or necklace center. For a dramatic look, surround them with a colorless diamond halo.  

Say “Yes”

Rose-cut black diamonds are perfect for an engagement ring, a trendy look, or a classic with a twist. Who would choose one? A fashion-forward customer who embraces her own sense of style, constantly seeking the unexpected. Or she could be a customer who wants to create a vintage design down to the smallest detail. Or perhaps she’s a customer who finds a rose-cut black diamond ring irresistible. Have one in your case, and you’ll be surprised by who it will attract.   

Mr. Big Gives Carrie the New Black

For you fans of Sex and the City, you know what I’m talking about. It happens near the end of the second movie when Big gives Carrie Bradshaw a fabulous five-carat black diamond ring. (Some people call it an engagement ring, but it’s actually their first anniversary!) And why did he choose the black diamond? His famous answer: “Because you are not like anyone else.” Doesn’t every woman want to hear that?  Though black diamonds had long established themselves as an homage to vintage style, Carrie’s ring — designed by Itay Malkin — has clean, modern lines made romantic by the contrast of the black center stone with the colorless gold and melee diamonds. If we needed any proof, this made it clear: black diamonds look gorgeous set in whatever style pleases your customer.



An Enduring Symbol

Whatever reason your customer chooses a rose-cut black diamond, the stone has potent symbolism. Like colorless diamonds, black diamonds embody love, fidelity, and eternity. But black diamonds go beyond that, symbolizing power, charisma, certainty, and passion. I think most women will love these meanings. 




Cursed Diamonds and Gemstones: All That Glitters Isn’t Gold

Last year, we covered gemstone superstitions — and that blog post has been trending online ever since. This year, just in time for the scariest day of the year, we’re going to dive into the fearsome folklore surrounding some (in)famous and cursed diamonds and gemstones.

Sinister Beauty: The Hope Diamond

No list of spooky stones is complete without the Hope Diamond. Known for its exceptional size, color, and history, the Hope Diamond is a hugely impressive stone.

Oh, and it’s cursed. Allegedly.

When Harry Winston donated the diamond to the Smithsonian Museum, many thought the country was doomed. Some individuals even urged President Eisenhower to reject the gift. How could such a remarkable diamond have such dark energy?

Well, it’s what Marie Antoinette was wearing when she was beheaded. And it was reportedly stolen from a statue of the Hindu goddess Sita. The origins of the curse vary, but people agree on one thing: that it is one cursed diamond. Take these examples of the rumored peril that has come to people who have been in possession of the Hope Diamond:

  • After stealing the diamond from Sita’s statue, the thief is said to have been killed by wild dogs.
  • Sultan Abdul Hamid of Turkey lost his throne.
  • Collector Philip Henry Hope’s family went broke, requiring the stone be sold to recoup losses, and his grandson died completely broke.
  • Evalyn Walsh McLean lost two of her children, and her husband was later committed to an asylum.

That’s just a sampling of tales, and while most are flat-out lies and the curse is exaggerated, who wants to take a chance? Best to leave it at the Smithsonian.

Men, Beware: The Koh-i-Noor

If you’re going to wear the 105.6-carat Koh-i-Noor Diamond, you better not be a man.

As the curse goes, “He who owns this diamond will own the world but will also know all its misfortunes. Only God or woman can wear it with impunity.” But those threatening words haven’t swayed people from wearing the Koh-i-Noor.

Believed to have been mined in India’s Kollur Mine in the twelfth century, the Koh-i-Noor has a long, bloody history. Here is but a sample of the misfortunes that have befallen the Koh-i-Noor’s owners:

  • Mughal emperor Babur lost his son to exile.
  • A later ruler, Shah Jahan, famous for building the Taj Mahal, spent the end of his days in prison — imprisoned by his own son, Aurangzeb.
  • Nadir Shah was assassinated.
  • Each of Nadir Shah’s successors were dethroned.

After centuries of poisonings, assassinations, civil wars, and invasions, the Koh-i-Noor eventually ended up with the British monarchy, where it sits today among the British Crown Jewels. However, this is not without controversy — the Indian government would like its diamond returned.

The Regent Diamond

The 140.64-carat Regent Diamond has a cruel, bloody history. Most known for decorating Napoleon Bonaparte’s sword, the Regent Diamond was stolen from India’s now-defunct Kollur Mine.

A slave hid the diamond in an open wound in his leg, then boarded a ship bound for Europe. The ship’s captain learned of the diamond and its whereabouts, so he murdered the slave. Afterward, the captain sold the diamond to an Indian merchant, and thus the curse began.

When the Crown Jewels of France were stolen in 1792, the Regent Diamond was among them. Napoleon got the stone in 1801, and Marie Antoinette had it later. And we all know what happened to her and Louis XVI.

Today, the Regent Diamond is displayed at the Louvre.

There are more cursed diamonds out there: the Sancy Diamond, the Taylor-Burton Diamond, and many more. But if you thought gemstones were safe, think again.

The Great Impostor: The Black Prince’s Ruby

Why impostor? Well, the Black Prince’s Ruby isn’t a ruby. Weighing in at a whopping 170 carats, it’s an irregularly cut cabochon spinel — and despite its impostor status, the Black Prince’s Ruby holds a position of high regard. Today, it’s set in the center of the Imperial State Crown of England.

Believed to have been mined in Badakhshan (today known as Tajikistan), the Black Prince’s Ruby first appears on record in the fourteenth century. Don Pedro the Cruel, ruler of Seville, Spain, plundered the gem from the Moors.

Then the Black Prince himself, Edward of Woodstock, had the stone, where it acquired its name. King Henry V had the gem next, having it set in his battle helmet beside real rubies, truly making this red spinel an impostor.

When King Charles I committed treason, he lost more than the stone, and the Black Prince’s Ruby passed from the British royal line to an unknown buyer. Charles II regained the stone later, but Colonel Thomas Blood nearly succeeded in stealing it during a 1671 heist.

The Delhi Purple Sapphire

The purported powers of sapphire include enlightenment, peace, and healing, yet devastation and despair have awaited all who’ve dared cross the Delhi Purple Sapphire.

Perhaps, that’s because there’s another impostor among us. But rather than a spinel masquerading as a ruby, this time, it’s an amethyst. No wonder the owners of the Delhi Purple Sapphire didn’t get to enjoy any of sapphire’s magical powers — they never had one to begin with!

Looted from the Temple of Indra during the Indian Mutiny of 1857, the Delhi Purple Sapphire is a gem allegedly cursed through thievery, by the Hindu god of war and weather. When the amethyst was taken from the temple, the ancient deity cast a curse upon the stone.

Afterward, the Delhi Purple Sapphire ended up in England, where it spelled trouble for all who owned it, from financial ruin to health problems galore, bad luck, and more.

Author Edward Heron-Allen sealed the gemstone inside a box and had it locked in a bank vault. Later, he gifted the stone to the Natural History Museum, with one stipulation: the box not be opened until three years after his death.

The Perilous Pearl: La Peregrina

La Peregrina, Spanish for “The Wanderer,” is a 50.56-carat pearl that originated from the Panama coastline in the sixteenth century. The then-administrator of the Panama colony gifted the pearl to Philip II, who subsequently gifted it to Queen Mary I of England.

Is Queen Mary I’s name familiar? If so, you may know her for her reign of terror that earned her the moniker Bloody Mary. She was rarely seen without La Peregrina — especially at executions. No doubt this pear-shaped pearl absorbed vile, violent energy.

The curse of La Peregrina is purported to be that of ruining the love lives of all who wear it:

  • King Philip II lived abroad for most of his marriage to Queen Mary I.
  • After Mary’s death, Philip proposed to her sister, who refused him.
  • Centuries later, Richard Burton purchased the stone for Elizabeth Taylor—who had seven marriages throughout her life. Richard was two of those.

As of 2011, La Peregrina belongs to an anonymous collector, who paid a whopping $11 million for the stone.

The Stolen Sapphire: The Star of India

As the world’s largest gem-quality blue star sapphire, the 563-carat Star of India is quite the coveted gemstone. So coveted, in fact, that on October 29, 1964, three thieves broke into the American Museum of Natural History in New York. They raided the gem hall, making off with millions of dollars’ worth of stolen gemstones — including the Star of India.

As the story goes, the display’s alarm batteries were dead. And the ill fortune went even further:

  • There was no security guard.
  • The windows were open.
  • The stone wasn’t even insured.

The thieves climbed in through the window and made off like the bandits they were.

Luckily, the Star of India was recovered not long after in the most unusual of places: a bus station locker in Miami, Florida. Not all the gemstones stolen with it were nearly as fortunate, however. Today, the Star of India is back at the American Museum of Natural History.

Hopefully, they’ve hired someone to regularly check the alarm system.

What’s the Verdict?

Are these stones truly cursed? We reached out to countless clairvoyants for confirmation, but they refuse to go on the record with a definitive answer.

But these tales do have some things in common: the stones were acquired through less-than-honorable means or have a bloody history. Perhaps, then, the curse is nothing more than a cautionary tale: don’t take what isn’t yours, and treat everyone with the kindness with which you want to be treated.

Certified Curse-Free Stones

We’re not daring enough to own any sinister stones — but we are daring enough to stock one of the industry’s largest diamond and gemstone selections. We offer more than 70 types of gemstones and diamonds in every size, shape, and color imaginable.

And don’t worry — we certify that all Stuller Diamonds™ and Stuller Gemstones™ were legitimately acquired and are thus curse free.


Enjoyed learning about the world’s most cursed diamonds and gemstones? Read our previous Halloween-themed posts regarding gemstone and jewelry superstitions.

5 Gemstone Superstitions and How to Use Them to Sell More Stones

6 Jewelry Superstitions and How to Use them to Your Advantage




Quick References Provided with New Diamonds & Gemstones Catalog

Earlier this month, we launched Diamonds and Gemstones 2020-2021, a 130-page catalog featuring Stuller’s comprehensive assortment of diamonds and gemstones. Visit our previous post to catch up on all the great highlights we have included in this latest edition.

Making this one of our most unique catalogs we have produced, the removable reference pages in the back of the book are ready to be used where you need them, when you need them. Including resources like a gemstone color wheel showcasing an assortment of complementary color possibilities, a poster showing best-selling round diamond and gemstone sizes and availability, and a variety of charts, tables, and information guides, this section of Diamonds and Gemstones 2020-2021 provides you with educational and reference material you can easily display in your store for both employees and customers. Explain industry concepts, such as the four C’s of diamonds or how stones are measured, to your customers or provide guides for your employees to refer back to on a regular basis with these easy-to-understand and illustrated resources.

Each of these reference pages are perforated for quick and clean removal from the catalog. If you prefer not to remove these pages, we’re happy to provide you with PDF copies of these pages for you to print for your personal use.

Click here to download your free Diamonds and Gemstones 2020-2021 reference pages.

From presenting the new additions to our Notable Gemstones™ and Stuller Diamonds® offerings to an updated visual aesthetic, Diamonds and Gemstones 2020-2021 provides you everything you need to quickly find what you are looking for in one of the industry’s widest selections. Visit our website for more information about the Diamonds and Gemstones 2020-2021 catalog.




All That Shimmers: Diamonds & Gemstones 2020-2021

Diamonds & Gemstones 2020-2021

As personalization continues to lead our industry, Diamonds & Gemstones 2020-2021 gives you all you need to quickly find that special stone within one of the industry’s widest selections. With 130 pages, this catalog features Stuller’s comprehensive assortment of diamonds and gemstones: beloved classics, on-trend favorites, and many new colorful options.

And in this latest installment, we’re doing things a bit differently.

Here are 5 cool updates in Diamonds & Gemstones 2020-2021

1. Beautiful New Look

This reimagined edition of our classic catalog is unlike anything we’ve ever done before. With its gorgeous new look, we’re sure you and your customers will love this catalog as much as we do. And, it will become your go-to resource for all things diamonds and gemstones.

2. New Products

Completely new to this catalog are Stuller Notable Gems™ and Stuller Diamonds® with grading reports. These two beautiful collections have their own chapter, setting the stage for a vast array of sparkling, stunning stones to come.

Dive in to discover a unique shape, cut, or color you may not have known we supply, such as fancy-color sapphires, multicolor tourmaline, salt-and-pepper diamonds, and so much more.

Diamonds & Gemstones specialty diamonds

3. Improved Navigation

We strive to make each new catalog better than the last, and this one is no exception.

You can look forward to a variety of navigational and other visual changes, starting with the beautiful, easily shoppable product pages and photography. From stone stock to services, you’ll discover everything you need within these six chapters.

Diamonds & Gemstones calibrated gemstones

4. Sourcing Map

Chapter six hosts a medley of cool and useful reference materials, and one of the things we’re most excited about is our sourcing map! You can see the global destinations our in-house experts visit to source only the best stones for you and your customers.

Diamonds & Gemstones sourcing map and color wheel

5. Gemstone Color Wheel

Our gemstone color wheel offers you a quick, at-a-glance comparison of various gemstones. With this handy reference, you can help your customers visualize the differences between gemstones of similar colors. Or, show them which colors would pair well.


The above is just a sampling of what awaits you in Diamonds & Gemstones 2020-2021. With discrete pricing, a references section that offers perforated pages, and captivating imagery, this catalog release is one of our most exciting of the year. And to build on that excitement, we’re running another catalog contest!

Color With Stuller

Show us your photo faves!

  1. From September 8 through October 9, 2020, take an image of your favorite photo from the new catalog.
  2. Submit that image to our Facebook or Instagram pages with the hashtags #HowIStuller and #ColorWithStuller. You can also email entries to Contest@Stuller.com.
  3. We will randomly select two winners to receive a $250 Stuller account credit toward the purchase of a diamond or gemstone!

Note: Winners must have a Stuller account in good standing and will be contacted via phone or email no later than October 14, 2020.


Flip through the pages in your copy, or browse the individual chapters online. You’ll be dazzled and delighted by what you unearth within!

Learn more about Diamonds and Gemstones 2020­-2021 on the Stuller website.