3D CAD software (like Rhino, Blender, MatrixGold, JewelCAD, ZBrush) is used to model gemstones with precise facets, symmetry, and proportions.

Parametric design tools (like Grasshopper for Rhino) let jewelers control cut parameters (table size, crown angle, pavilion depth, girdle thickness, etc.) so the gemstone can be modeled just like real gem cuts (round brilliant, emerald cut, princess, etc.).

Rendering engines (Cycles, V-Ray, KeyShot) simulate light dispersion, brilliance, and fire, making the diamond/gemstone look photorealistic.

3D printing / CNC: Once modeled, the gemstone (or a placeholder stone) can be output for jewelry prototyping.