The modern princess cut — a square brilliant-cut diamond with unrounded corners — was patented in 1979 by Betazel Ambar and Ygal Perlman. Their US Patent 4,168,604 described a square or rectangular stone with brilliant-style faceting adapted to a non-circular outline, producing a diamond that retained much of the optical performance of a round brilliant while fitting the natural geometry of rough diamond crystals far more efficiently. The patent represented the culmination of a decade of work on square brilliant cutting that had begun with predecessor designs in the early 1960s.
The genius of the princess cut — then called by several names before "princess" became the industry standard — was essentially economic. Diamond rough occurs naturally in octahedral (eight-sided) crystal forms. Cutting a round brilliant from an octahedron wastes significant material at the corners. The princess cut, with its square outline, can be cut from half an octahedron with minimal waste. Two princess cuts can be produced from a single octahedral rough where only one round brilliant of comparable weight could be extracted. This yield advantage is the structural explanation for the princess cut's historically lower per-carat price relative to rounds.
The princess cut's unrounded corners are both its yield advantage and its structural liability. Diamonds cleave along specific crystallographic planes, and a pointed corner concentrates stress in ways that rounded or cropped corners do not. A princess cut that receives a sharp lateral impact — especially at a corner — is at higher risk of chipping than a round brilliant, an Asscher with cropped corners, or an oval with no corners at all. This is not a flaw of the design — it is the trade-off Ambar and Perlman knowingly accepted in exchange for yield efficiency. The solution is a proper four-prong setting where each prong covers a corner.
The princess cut dominated the fancy shape market through the 1990s and 2000s, driven by its optical performance (near-round brilliance), its geometry (square outline with strong visual character), and its price advantage (yield efficiency). It has since been surpassed in popularity by cushion cuts and ovals, as consumer preferences shifted toward softer silhouettes and vintage aesthetic references. The princess cut's pricing has reflected this shift — per-carat prices have softened relative to peak, which can represent genuine value for a buyer who likes the look.
| Factor | What to check | Target |
|---|---|---|
| Length-to-width ratio | Square vs. rectangular face-up | 1.00–1.05 for square appearance |
| Depth % | Deep cuts hide mass below girdle | 64–75% |
| Table % | Balance of brilliance and crown height | 67–75% |
| Corner condition | Check for chips at corners under magnification | No chips; confirm from report clarity plot |
| Setting requirement | Four-prong minimum to protect corners | Confirm setting covers all four corners |
| Clarity | Inclusions visible in corner facets | VS1–VS2 minimum; corners visible in setting |
Ambar and Perlman solved a real problem — how to get brilliant-cut optical performance from a square stone while maximizing rough yield. Their patent produced the best-selling square diamond of the 20th century. The trade-offs they accepted — sharp corners requiring protected settings, slightly lower clarity forgiveness than rounds — are well worth understanding before purchase, but they are not reasons to avoid the cut. The princess cut at its best is a strong performer with a distinct visual character and an often-favorable price.