In modern-day fine jewelry, the most commonly used stone material is round brilliant-cut (RBC) diamond melee. Widely available in a multitude of sizes, the application of RBC melee in a jewelry computer-aided design (CAD) model is limited only by the creativity of and communication between the designer and CAD modeler.
Most designs that are submitted for CAD creation will include requested melee sizes. At times, following the outlined requests can produce a great look, but more often than not, small tweaks in diameter size will create a superior aesthetic and technical layout.
While it’s handy for a designer to think about and include recommendations for melee sizes with their sketches for a piece, the ability to finely tune the choice is more easily adjusted and realized with the aid of CAD programs. If you can leave the final call on diameter size until options have been fully evaluated by a modeler, you will be able to produce a layout that is as pleasing to look at as it is to manufacture.
Jewelry designers and modelers tend to think about RBC melee dimensions in full tenths of a millimeter (e.g., 1.30 mm, 1.40 mm, 1.50 mm, etc.). These are the sizes that are commonly marketed at wholesale and are used as defaults in CAD programs. However, splitting the difference into half-tenths of a millimeter (1.35 mm, 1.45 mm, 1.55 mm, etc.) can allow for advanced improvements in the spacing between stones and overall layout.
The images shown here depict the same halo design laid out using three different sizes of RBC diamond melee. Figure 1 uses 1.30 mm, Figure 2 uses 1.35 mm, and Figure 3 uses 1.40 mm RBC melee. Each halo can successfully be bead-set in metal by a stone setter, but by using the 1.35 mm diameter choice in relation to the center stone’s prongs, the best visual and technical symmetry is created. This option would be lost if the half-tenth sized stones had not been considered.
In general, most diamond melee suppliers will not list their goods at half-tenth sizes, leading one to believe they are not available. However, RBC melee that is broken down into a smaller diameter range can usually be ordered by special request.
It’s rare to find a supplier that refuses to accommodate this kind of simple inquiry. When asking for specifically sized melee, it is good practice to let the supplier know ahead of time which diameter range you find acceptable: “I expect RBC melee to be within 0.03 mm of the desired size.” (In the case of asking for 1.35 mm RBC melee, any stones between 1.32 and 1.38 mm would be within an adequate range.) Provided that the CAD model has been prepared properly, this will ensure the stone setter won’t run into spacing issues during the setting process.