OLD-CUT DIAMONDS AND RECUTTING CALCULATION
There are several cases when recutting of a diamond is desirable: the stone is unproperly cut, has distorted geometry features or irregular proportions, has an old cutting style, or is badly damaged. Recutting can make such a stone more attractive. Sometimes, recutting also improves clarity. It should be noted that recutting is always accompanied by a more or less significant weight loss. Since weight is one of the criteria determining diamond price, recutting is not always profitable.

Recutting results in a decrease in the total depth or diameter of a stone (sometimes, both parameters).

Before recutting, the following main questions should be answered:

  • How much can the stone be improved?
  • What is the weight loss?
  • How will the price change?

Appraisal of old-cut diamonds, stones with significant proportion and symmetry distortions, and damaged stones can be performed by the recutting calculation method. The diamond price is derived as that of the stone which can be obtained as a result of recutting.

Round or near round diamonds, considered as candidates for recutting, can be divided into four categories:

  • Stones with a high crown and deep pavilion;
  • Stones with a shallow crown and shallow pavilion;
  • Stones with a high crown and shallow pavilion;
  • Stones with a shallow crown and deep pavilion.

Fancy-cut stones are also recut in some cases.

The formulas given below can be used for the estimation of the weight of a recut diamond. If the size of the future diamond is determined by its diameter, the total depth of the stone may vary depending on accepted standards or client requirements. Thus, the coefficients in the formulas can be changed to select desirable proportions for the future diamond.

Shallow crown and deep pavilion

After recutting the total depth of a stone is measured with a proportionscope:

  • Determination of the total actual depth; (%)
  • Determination of the actual pavilion depth with a proportionscope.

The total depth after recutting = actual total depth - actual pavilion depth + 43%

Weight after recutting = (actual average diameter)2 x determined total depth after recutting x 0.0061

If it is necessary to reduce both the total depth and diameter by recutting, proportionscope should be applied to predetermine the crown height, pavilion depth, table size, and girdle thickness.

Weight after recutting = predetermined total depth x (predetermined girdle diameter)2 x 0.0061
Shallow crown and shallow pavilion

Actual depth = depth after recutting

Selection of the percentage of the total depth after recutting:

  • Select the table size and crown angle;
  • Select the average girdle thickness;
  • Select the percentage of the pavilion depth;
  • Sum these percentage values to obtain % of the total depth after recutting.

Diameter after recutting = actual depth/0.58

Weight after recutting = (predetermined diameter after recutting)2 x total depth after recutting x 0.0061
High crown and deep pavilion

To determine the parameters of a stone after recutting, a proportionscope should be used:

  • Select the pavilion depth 42-43%
  • Select the girdle thickness and crown height

Depth after recutting = predetermined pavilion depth + predetermined girdle thickness + predetermined crown height

Diameter after recutting = predetermined depth/0.58

Weight after recutting = (predetermined diameter after recutting) 2 x predetermined depth after recutting x 0.0061
Recutting of fancy shapes

The following conditions should be taken into account in recutting of fancy-cut stones:

  • The minimum weight loss in recutting;
  • Appeal and popularity of the seletced recutting shape;
  • Price deductions established for the selected shape.
Recutting of old-cut diamonds

The weight of old-cut diamonds is calculated as follows:

  • Diameter after recutting = minimum actual diameter
  • Depth after recutting = minimum diameter x 62.2%
  • Weight after recutting = (diameter after recutting)2 x depth after recutting x 0.0061