Ovelian — Oval-cut gemstones and diamonds as a buying | ovelian.com
How length-to-width ratio and pavilion depth create or remove the central bow-tie, with the ratios to favour.
The length-to-width ratio of an oval is its length divided by its width, measured on the face-up outline. The classic band runs 1.30 to 1.50. Inside that band, 1.40 to 1.42 reads most balanced; at 1.50 and above the outline is clearly elongated.
The bow-tie is a dark bow-shaped band lying across the centre of the stone. It appears when the ratio is too long or the pavilion is too shallow: in both cases the central pavilion facets throw light sideways instead of back up through the table, and the middle of the stone goes dark.
Ratio and bow-tie are linked but not identical. Two stones at 1.42 can differ sharply, because the deciding variable is how the pavilion was cut for that outline, not the outline alone. A longer outline simply gives the shallow-pavilion problem more room to show.
On narrow screens, swipe or scroll the plate sideways.
Judge the bow-tie face-up under neutral white light, tilting the stone slowly. A faint shadow that moves as you tilt is normal light behaviour. A fixed dark bow that stays dark while the tips keep flashing is the defect to reject.
The ratios to favour are therefore 1.40 to 1.42 for balance, with anything at 1.50 or above treated as clearly elongated and checked for a bow-tie before purchase. Shorter stones near 1.30 carry less bow-tie risk but give up some of the face-up spread advantage described on the main page.
When comparing two stones, match the ratio first and then compare the centre under the same light. That isolates the pavilion as the variable, which is where the bow-tie actually comes from.
Further reading