2022.11.11 Jewellery Column

An Engagement Ring Crafted with Sparkling, Beautiful Diamonds Polished by Artisanal Cutting Techniques

The Story of Polishing Artisans' Techniques That Bring Out the Beautiful Brilliance of Diamonds

Known as the "king of gems," diamonds symbolize enduring radiance, making them a perfect emblem for wedding and engagement rings.


Sparkling diamond roughs are also gifts from nature. They crystallize deep underground over a period of more than a billion years and are brought near the surface by magma, then mined from diamond mines.



These rough diamonds don’t start out sparkling. They undergo a transformation through skilled cutting and polishing before they become the sparkling king of gems "Diamonds" we all recognize.



So, how is the sparkle of diamonds, which uplifts spirits just by being seen, created?


In this article, we will introduce the polishing process of diamonds, which is actually not well known.

Capturing the Essence of the Raw Stone in the "Positioning" Process

The first crucial step in diamond processing is "positioning."


Each rough diamond is unique.


For each rough stone, the goal is to judiciously determine how to cut it in a way that avoids inclusions as much as possible while retaining weight and ensuring the resulting loose diamonds has beautiful brilliance.


Witnessing the Positioning Process

We had the opportunity to learn about this rarely seen process from Mr. Sekine of Eiwa Material.


Initially, the raw diamond is traced using specialized machines. Before machines were developed, it was common to manually change the angles of the rough stones, photograph them, and analyze the images. This was a very labor-intensive process. However, I've heard that accuracy and efficiency have significantly improved with the current technology.



The machine scans the raw diamond and displays its three-dimensional information as a traced image.



Furthermore, suggestions are made on how the rough stone should be processed, including the positioning strategy.



This data serves as a sort of diagnostic report, akin to a blueprint for diamond processing.


Artisans assess the optimal positioning strategy in accordance with the internal structure of the rough stone, such as inclusions.



The shape and internal structure of rough stones vary individually, resulting in differences in the number and size ratio of diamonds that can be extracted. In the case of the rough stone displayed in the image, the cutting of two loose diamonds of different sizes was proposed.


Following each diagnostic result, skilled craftsmen cut and polish the diamonds, creating the ideal finished loose diamonds.

Understanding the Best Positioning Process

Optimal positioning means maximizing the use of the raw diamond. This requires the high skill level of experienced polishers.



For example, if it's possible to obtain a diamond larger than 2.0 carats, the priority is to preserve its size as much as possible. Conversely, if the diamond is less than 0.5 carats, the focus shifts towards maximizing its brilliance and color beauty over size, making it crucial to carefully consider the inclusions.


Such discernment, highlighting each stone's unique charm, is the mark of a skilled polisher.



With expert hands, the following types of loose diamonds are produced:


*Polishing without loss, retaining weight

→ large carat diamonds are produced

→ additionally, loose diamonds (small diamonds under 0.1 carats) are obtained


*Avoiding inclusions and scratches for effective light entry and reflection

→ the clarity (transparency) increases, enhancing the sparkle


Understanding Inclusions

Natural diamonds are formed deep underground while growing. Inclusions are other mineral crystals mixed into the diamond or irregular atomic structures that occur during the diamond's crystal growth process. Inclusions and blemishes can obstruct light, thus impeding the diamond's sparkle.


The cutting of a diamond is performed based on precise calculations to enhance its sparkle by allowing light to enter and reflect efficiently. By minimizing the impact of inclusions and blemishes and preserving as much of the rough stone as possible, a larger and more beautifully sparkling loose diamond is achieved.


Seeking Greater Brilliance

In Japan today, there is a tendency to prefer diamonds that are modest in size but have beautiful sparkle, making the cut that brings out a brilliant and sparkling shine very important.



Although diamonds come in a variety of shapes such as round, square, and heart, the Round Brilliant Cut is known for producing the most sparkle.

The Round Brilliant Cut of a Diamond

When people think of diamonds, the Round Brilliant Cut often comes to mind.


The Round Brilliant Cut is a cutting technique developed in the 20th century that creates numerous facets, up to 58, on a diamond. By polishing these small surfaces, it generates countless reflections of light within the diamond, becoming the key to unlocking its sparkle.



The shape, size, symmetry, and angles of the facets and other parts are precisely determined to enhance the diamond's sparkle. The process of cutting and polishing these facets is carried out by the skilled hands of artisans.



Artisans who control their techniques and meticulously polish diamonds with experience and skill produce Triple Excellent (3EX) diamonds. Among them, only a handful of craftsmen are capable of creating the even more refined Five Excellent (5EX) diamonds.



Only a very limited number of polishing artisans can discern the differences in hardness and characteristics of each diamond rough that are not apparent in data, using all senses including the feel and sound transmitted to their fingertips while actually polishing. The diamonds polished with such delicacy possess symmetry.






One feature illustrating symmetry is the “Hearts & Cupids” pattern. In the video, the 5EX diamond on the left displays eight evenly shaped and spaced white arrows.


When compared to the EX cut diamond on the right, one can observe not only differences in the shape of the arrows but also in the sparkle. Diamonds displaying both arrows on the crown side and hearts on the pavilion side are known as Hearts & Cupids diamonds, indicating high symmetry.


The Sparkle of Diamonds Brought Out by the Skill of Artisans

We've talked about the cutting process that enhances the sparkle of diamonds, but it might be difficult to grasp what specific tasks are involved, isn't it?



Therefore, we will introduce the experience of diamond polishing by Ayu Takahashi, the representative of ith, supported by Mr. Sekine, who is also an excellent diamond cutter with superb skills.

The Diamond Polishing Experience


The tools used for polishing are simple, with a structure similar to that of a record player. To give an analogy, imagine setting the diamond at the tip of a record needle and the polishing disc as the record itself. The diamond is then smoothed by pressing it against the rotating polishing disc.



The tools used and the process itself are surprisingly simple.


However, without a thorough understanding of the diamond's structure and accurately setting it in the desired direction for cutting, it is impossible to precisely carve out a symmetric diamond. The mechanism is straightforward, but the process demands high-level artisan skills.


To minimize loss and achieve a smoother finish, it is crucial to carefully assess the rough stone and set it at the optimal angle for cutting the small diamond into a 58-facet gem.



The actual polishing process involves the diamond gradually being cut down, with vibrations transmitted to the fingertips.


However, while it is possible to cut, determining how much has been cut or whether it has been smoothly polished based on sound and touch is not easy.



Professional artisans repeatedly polish the diamond, changing facets as they go. Through this process, the diamond gradually gains its sparkle.



When a skilled craftsman like Mr. Sekine works on the diamond, the interaction between the diamond and the polishing disc polishes both, resulting in a smoother disc after polishing.


However, when a novice polishes, additional deep grooves in the direction of the disc's rotation can be seen, in addition to the intended radial lines.



Crafting the tools is another sign of an excellent artisan. Beyond just polishing discs, craftsmen often create their tools.



Key Points to Support Superior Cutting Techniques

・Assessing the raw stone
・Determining the direction of polishing
・Understanding the crystal structure (identifying cuttable and harder parts)
・Creating and maintaining tools/discs
・The skill level of the polisher


The Brilliance that Illuminates Life

Understanding how diamonds are processed can make these gems feel more accessible, even if you feel unsure about discerning their differences.



The high grades and prices of diamonds, such as 4C ratings or 5EX diamonds, reflect the careful work of artisans. As you learn more about the evaluation criteria, choosing a stone that feels more beautiful and valuable to you becomes easier.


Like meeting people, each gemstone possesses unique allure. At ith, our primary focus is ensuring that the chosen diamond is truly desired by the wearer. We offer a wide range of diamonds with various characteristics, including high-quality diamonds that you can trust.


When you visit our atelier, enjoy the experience of finding the diamond that feels destined for you. Our concierges eagerly await your arrival.


Learn more about Diamond Features

ith's Engagement Ring Collection

List of ith Ateliers



An Engagement Ring Crafted with Sparkling, Beautiful Diamonds Polished by Artisanal Cutting Techniques