Rough Diamond Evaluation Methods

This page is dedicated to describing evaluation methods for larger rough diamonds. Please note that this page only serves as an introduction to the practices on the rough diamond market, we do not recommend purchasing rough diamonds without adequate training and guidance.

To purchase rough diamonds at Ajediam:  

If you are interested in buying at Ajediam, please contact our team directly by email, and indicate what you are looking for, your budget, and when you would like to come for a viewing.

A step-by-step example of rough diamond evaluating and pricing for larger diamonds

Professional rough diamond buyers typically aim to estimate the potential yield of polished diamonds in terms of shapes, sizes, colors, and clarity that can be obtained from the rough diamond. This estimation usually involves considering several scenarios, with the ultimate goal of identifying the scenario that presents the least risk and the most profitability. Typically, professional buyers may consider up to three different scenarios. Please follow along as we take you through each step of sorting and evaluating rough diamonds.

Rough Diamond Provenance

Each country produces diamonds of various types, and there exists a market for each of these types. The fundamental prerequisite for selling rough diamonds is the presence of appropriate documentation, which includes certification from the Kimberley Process and traceability documentation of the diamond’s origin and journey from the mine to the current point of sale.

Rough Diamond types

There are various types of rough diamonds, each with its own characteristics and potential outcomes during the polishing process. One of the most desirable types is the “makable” shape, which means that the rough diamond already has a shape that it can be cut into. This is particularly advantageous, as there is usually less loss of weight during the polishing process compared to other shapes.

Another type of rough diamond is the “sawable”, which means that the rough diamond needs to be cut before it can be polished, and will likely result in at least one or two stones. The number of stones that can be obtained from a sawable rough diamond largely depends on its size, shape, and internal characteristics.

“Cleavage” rough diamonds have a lot of internal cleavages, meaning that the stone will split in specific directions when cut. As a result, a cleavage rough diamond can often be cut into multiple smaller stones.

Lastly, “Macle” rough diamonds are typically flat and long and often result in triangle shapes or rose cuts. The outcome largely depends on the shape of the rough diamond, and the skill of the diamond cutter.

Understanding the type of rough diamond shape is important for diamond cutters and buyers.

Rough diamond weight and size 

While the sorting process for larger diamonds only requires weighing the rough stones on a carat scale, sorting the smaller goods involves a set of sieves with varying mesh sizes. The rough diamonds are placed on the top sieve and shaken until they pass through the appropriate mesh size, indicating their size range. This process allows for quick and efficient sorting of large quantities of small diamonds.

Rough Diamond color categories

Experienced professionals in the rough diamond trade use specialized equipment known as a color machine to accurately identify the color of a diamond, provided that the diamond has not been coated. Coated diamonds have a dark coating on their surface, masking a lighter color on the inside. Such diamonds need to get a small area polished flat on the surface through the coat so that one can identify the color by eye.

In order to sort rough diamonds by color, they are generally categorized into a few major color groups. These groups include white diamonds, ranging from D to J in color; cape diamonds, ranging from K to M; yellow diamonds, with a color grade of M or higher; brown diamonds. Fancy colors such as blue, pink, green, orange, purple, and red are sorted into separate categories.

Rough Diamond clarity 

Rough diamonds can have both external and internal inclusions, which affect their value and potential for polishing into high-quality diamonds. In order to assess the clarity of a rough diamond, professionals use various tools and techniques.

For larger rough diamonds, a Sarine machine may be used to examine the internal structure and potential inclusions. This machine uses advanced imaging technology to create a 3D model of the diamond and identify any potential areas of concern.

However, for smaller rough diamonds, clarity is typically checked manually using a loop. This involves inspecting the diamond under magnification to identify any visible inclusions or blemishes.

Minimizing risk: Observing tension in Rough Diamond

When a diamond breaks or cracks, it usually happens during the laser cutting process. To minimize this risk, we analyze and detect tension in stones with the Polariscope. While it is rare for diamonds to break, it can occur when the stone has internal tension and is subjected to high pressure at specific locations. This tension can run along existing inclusions such as feathers, but not always.

To protect your investment, you can take out insurance to cover the risks while cutting and polishing your diamond. The cost of insurance typically ranges from 0.5% to 3% of the diamond’s value, depending on whether it has tension or not. By having insurance, you can mitigate the financial impact of any unforeseen incidents that may occur during the diamond-cutting process.

Evaluation of the potential outcomes

Once a rough diamond has been assessed for clarity, the next step is to determine the most profitable potential outcome for the diamond. The goal is to achieve optimum clarity and shape size ratio for polishing the diamond. This requires a careful balance between maximizing the size of the resulting polished diamond and minimizing any inclusions or blemishes that could reduce its value.

Usually, manufacturers will consider several cutting scenarios before planning. It is worth noting that manufacturers often base their profits on the small extra stones that can be polished from the same rough diamond. This is because the pricing of rough diamonds is highly competitive, so the main polished stone or stones that will be cut from a rough diamond will usually only cover the costs.

Any additional smaller cuts that can be obtained from the same rough stone represent potential profit for the manufacturer. Therefore, maximizing the number and quality of extra stones obtained from a rough diamond is an important factor in determining the ultimate profitability of a given diamond.

Learning about Rough Diamonds

There is no better way to learn about rough diamonds than on the field, but it can be hard to get into the industry without a contact. Schools are the second best option and they can open doors to a closed industry and help you make your first contacts. Several schools offer a rough diamond program but we recommend the  HRD Antwerp Rough Diamond Course.

The HRD Antwerp Rough Diamond Course is designed to provide comprehensive knowledge and skills in rough diamond sorting and evaluation. The course covers a wide range of topics such as diamond formation, characteristics and properties of rough diamonds, diamond mining and production, and rough diamond trading.

Participants are taught how to use various tools and equipment such as microscopes, tweezers, and sieves to sort and evaluate rough diamonds based on their size, color, clarity, and shape. They also learn how to use advanced technologies such as spectrometers, X-ray machines, and Sarin machines to detect and analyze the properties of rough diamonds.

The course also covers the diamond value chain, pricing mechanisms, and market trends. Participants are exposed to real-life scenarios and case studies to simulate the experience of a professional rough diamond trader.

At the end of the course, participants are required to pass a comprehensive examination that tests their knowledge and practical skills. Successful candidates are awarded a certificate that recognizes their proficiency in rough diamond sorting and evaluation.