The Lazare Brilliant, sometimes branded as the Ideal Cut, is a proprietary cutting standard for round brilliant diamonds developed and commercialised by Lazare Kaplan International (LKI). The standard is a refinement of the proportions described by Marcel Tolkowsky in his 1919 doctoral dissertation 'Diamond Design: A Study of the Reflection and Refraction of Light in Diamond,' which established for the first time the mathematical basis on which the round brilliant could be cut to maximise the return of light through the table.

The Tolkowsky calculation

Tolkowsky's analysis, published when he was twenty-one and a student at the City and Guilds Engineering College in London (now part of Imperial College), used basic geometric optics to determine the angles at which light entering the table of a round brilliant diamond would be totally internally reflected by the pavilion facets and exit through the crown facets back toward the observer. The principal results were a crown angle of approximately 34.5 degrees, a pavilion angle of approximately 40.75 degrees, a table size of approximately 53 percent of the girdle diameter, and a total depth of approximately 59.3 percent.

Tolkowsky's work was theoretical and assumed an idealised diamond with perfect proportions and finish. It established the framework within which later refinements would operate but did not in itself provide cutting tolerances or a commercial standard.

Lazare Kaplan and the commercial cut

Lazare Kaplan Sr., a Belgian-Polish diamond cutter who emigrated to the United States in 1919, was among the first cutters to systematically apply Tolkowsky's principles to commercial production. Kaplan's workshop in New York refined the cut through the 1920s and 1930s and made it a proprietary feature of the Lazare Kaplan operation. The brand name 'Lazare' as applied to ideal-cut round brilliants dates substantially from the postwar period, when the firm shifted from primarily wholesale cutting to branded retail distribution of its own cut diamonds.

The Lazare Brilliant standard, as commercialised, specifies tighter tolerances than Tolkowsky's theoretical optimum allows. Crown angles are typically cut between 34.0 and 34.9 degrees; pavilion angles between 40.6 and 41.0 degrees; table sizes between 54 and 57 percent; and total depths between 59 and 62 percent. The standard also specifies symmetry tolerances (variation in pavilion main angles of less than 0.4 degree, eight equal pavilion mains, eight equal crown mains, etc.), polish tolerances, and girdle thickness limits.

Branding and inscription

From the 1980s onward, Lazare Kaplan introduced the practice of laser-inscribing the firm's name and a unique serial number on the girdle of each Lazare Brilliant. The inscription is barely visible to the unaided eye but readable under 10x magnification and serves as a permanent identification mark. The practice has since been adopted by multiple branded-cut programmes (including A. CUT ABOVE from Whiteflash, Hearts on Fire, and others) and has become the standard for branded ideal-cut diamond identification.

Comparison with other branded ideal cuts

The Lazare Brilliant is one of several branded ideal-cut programmes that occupy the top of the round brilliant market. Hearts on Fire (founded 1996), A. CUT ABOVE (Whiteflash), Solasfera, the Tiffany Setting (Tiffany & Co. has not historically branded its cut as such but applies internal standards), and others compete in the same space. The differences between programmes are typically narrow, involving small variations in proportion tolerance, optical-symmetry assessment (e.g., the Hearts and Arrows pattern under specialised viewers), and marketing positioning.

Trade significance

The Lazare Brilliant established the precedent that a branded cut could carry a price premium beyond the underlying diamond grade. The premium varies but is typically 10 to 30 percent over an unbranded GIA Excellent cut of similar weight, colour, and clarity. The premium is justified to consumers by the assurance of tight proportional consistency and by the optical performance that follows from it; whether the premium reflects a corresponding increase in objectively measurable optical performance is a question that the trade and the laboratory community continue to debate. GIA's introduction of the Excellent cut grade in 2006, based on the firm's own decade-long study of round brilliant proportions, narrowed but did not eliminate the gap between branded and unbranded ideal-cut diamonds.