Jagged octahedron, 10.19 carats, from Congo


Stronger brightness can compensate for the lack of color

This octahedral diamond crystal was found in the Mbuji Mayi region of the Democratic Republic of Congo. Its surface has corrosion pits, giving it a jagged appearance, just like a saw blade. Mbuji Mayi is located near the center of Kasai East Province, where diamonds are produced. There are countless alluvial deposits there, and many private operators are involved in mining diamonds. About 90% of the diamonds found here are industrial-grade, but Mother Nature occasionally creates a surprise. For example, in 1993, a rough gem-quality diamond weighing 777 carats was found here. The final product of this diamond is De Beers Millennium Star, which weighs 203 carats, D color grade, and FL clarity.



The rough diamond was found in the Paqika area, which is very different although it is located only 200 kilometers west of Mbuji Mayi. Because 90% of the diamonds produced here are gem-grade and only 10% are industrial-grade, but crystals larger than 20 carats are rarely produced.
Among the four opinions on cutting this rough diamond, we finally decided to polish it into two round brilliant cuts. Since the color of the crystal is located at the boundary between the J color and the K color, the round bright cut will increase the probability of getting a color higher than the J color. The brightness of the round bright cut is stronger and more balanced, which can make colors and blemishes look less obvious. But in emerald and cushion cuts, the color is more likely to gather in the corners, and the color is more obvious.
The final result is a slightly lower output. Among them, the larger diamond weighs 3.16 carats, has a J color, and has an SI level of clarity, which is the same as expected. Like this crystal, it is a common practice to cut a rough diamond of J or K color into round brilliant cuts to maximize the display of potential beauty.



When the foggy or coating appearance of a diamond makes it impossible to observe its internal features, we will polish a small surface called a "window", and then we can evaluate the internal condition of the diamond and detect the influence of all inclusions. However, since it is impossible to open the window when buying a diamond for the first time, buyers have no choice but to speculate. Therefore, when purchasing rough diamonds, it is extremely important to be familiar with the characteristics of diamonds from various sources. Experienced rough diamond buyers have an intuition that allows them to judge the quality of the diamond even when they cannot see the internal characteristics of the diamond. According to their experience, they know whether a special type of rough diamond with a known source has high or low clarity, or whether their appearance color can be improved by polishing.
Although diamonds from different sources have different characteristics, and diamonds from the same source often have similar characteristics, there is no guarantee that they will be successfully distinguished from other sources. There are no experienced substitutes when trading rough diamonds.

Basic polishing procedure

The following figure shows the basic steps of a rough diamond from an octahedron to a polished round brilliant cut diamond.



First, saw the octahedron into two parts. Normally, the saw surface will be the finished countertop. Then, grind the corners of the diamond to get the round shape of the diamond. During the rough grinding process, the diamond is fixed on the end of the spinning lathe and is aligned with the other one.
After rough grinding, use a polishing machine filled with diamond powder and oil to start cutting and grinding the small surfaces. The first stage is called "blocking", and the larger main facets have been carefully polished, including eight facets on the upper part (crown) and eight facets on the bottom (pavilion). At this time, the diamond is a single multi-faceted cut with 17 facets (including countertops). The thickness of the girdle, whether the bottom facet will be cut at the bottom tip of the pavilion, and the size of the bottom facet will all be determined at this stage.
Finally, the small upper waist and lower waist facets will be completed in the "multi-faceted process" stage, and finally, 57 or 58 faceted round bright cuts are completed. In recent years, with the introduction of modern technology and computers, many processes have become automated. However, no matter what technical advantages appear, diamonds are used to polish diamonds.

When the surface of the rough diamond is windowed, you can use a microscope to observe the internal characteristics of the diamond. The location and size of each inclusion are marked in the computer, and the polishing simulation is carried out at the same time. The saw surface shown in this figure is determined by such a simulation. Due to the structure of the diamond crystal, there are only limited directions that can be used to cut diamonds physically, but laser technology makes it possible to cut obliquely, which ultimately increases the output of diamonds. Here we can see that the saw surface corresponds to the tabletop of the big diamond.



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