Girdle (gemstone)
The narrow band around the widest part of a faceted gemstone, separating the crown from the pavilion.
Girdle thickness and finish
Labs grade girdle thickness from extremely thin to extremely thick. A very thin girdle can chip, while a very thick one adds weight without adding visible size. Girdles can be faceted, polished or left with a fine frosted finish called bruted.
Why it matters for settings
Every setting grips the stone at or just above the girdle. Prongs seat into small notches at the girdle, bezels wrap around it and channels hold it in grooves. That makes the girdle diameter the key measurement in CAD, because the seat must match it.
Girdles in CAD
When you place a stone, align the girdle with the seat height in the setting. A girdle sitting too high leaves the stone looking loose, while one sitting too low buries the crown in metal. Check from a side view, ideally with the metal shown semi-transparent or in a section view, before you export.
Rendering girdles
The girdle is usually hidden by the setting, but in side views of prong settings it shows as a thin bright or grey line. A frosted girdle should look slightly matt compared with the polished facets. In most product images this detail is too small to see, so focus on correct seating rather than girdle texture.