(CR-57, "Standard Round Brilliant cut", "Round Brilliant cut")
Cut of this kind has a circular plan shape, the type of the cut diamond (wedge-shaped). Faceted stone has 57 facets, 33 facets of the crown (octagonal pad, the top eight wedges, eight main crown facets of the diamond-shaped, sixteen pairs of wedges) and 24 facets of the pavilion (sixteen pairs of wedges and eight main facets in the form deltoid).

The main elements of the Round brilliant cut diamond ("CR-57")
(parameters are shown for the optimal cut shapes)

The calculation of the weight

Calculate the weight (in carats) of the standard round brilliant cut for diamond is produced by the basic formula:

M = D2 x H x k

where M – mass cut diamond, D – average diameter of the cut of a diamond, measured on the main faces of the crown, H is the height of the diamond, k – conversion factor metric measurements using the volume to mass, taking into account the geometry of the cut, and the density of diamond having a value of 0,00612.

For stones with the inability to measure the height of the normative estimated weight can be calculated by the formula:

M = D3 x k

where k is the conversion factor metric measurements using the volume to mass, considering the standard geometry of the cut, and the density of diamond having a value of from 0,00355 to 0,00375 (with an average – 0,00365).

More precisely, a weight is determined taking into account the amendments on the thickness of the girdle, bulge cut, size caletta, the ratio of the proportions of the cut.

Valuation of diamond is the round brilliant cut can be made on the basis of data for the respective cut price indices and price lists: Rapaport Diamond Report the IDEX Diamond Price Index, The GemGuide, Palmieri's Market Monitor.

The type of cut "Standard Round Brilliant cut" appeared in the early XX century. Most of the literary sources include the first description of round brilliant-cut diamonds to the period 1890-1910 years as modifications of the old diamond cut "Old mine cut" with 57 facets and caletti. In 1916 Frank Wide (Frank Wade) described the design of round brilliant cut diamonds, in 1919, Belgian diamond cutter Marcel Tolkowsky (Marcel Tolkowsky) in his book "Diamond Design" published mathematical calculation supporting the optimal parameters for the round brilliant cut.Later, 1939-1940, William Appler (Wilhelm Friedrich Eppler) proposed a somewhat different proportions of a brilliant cut (Practical Fine cut). They were received on the basis of mathematical calculations based on the practical component.

The parameters of the modern cut diamond Kr-57 cut was determined experimentally to 1968, with certain amendments, accepted as perfect in the world at present.