Guy Borenstein

Meet Guy Borenstein: Stuller’s New Senior Gemologist

Elizabeth Raffel interviews Stuller's expert in diamond and gemstone technology.


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.