To cut a gemstone using the precision cutting method, the diagrams contain precise information that will allow the creation of a pre-designed pattern.

It is obvious that the result inevitably varies from one stone to another depending on the starting potential of the material: color, inclusions, transparency, etc. However, this issue is more related to the choice of rough than to the cutting plan itself.

In this article, we will therefore explain, in broad terms, how a cutting plan works, and for this, we will use the diagram of a round brilliant cut as an example.

Here is the design of a round brilliant cut plan:

Here is what the first box gives us as information:

Angles for R.I = 1.540: This indicates that this diagram is drawn for a gemstone with a refractive index of 1.54. You can therefore understand that a quartz could be cut using this diagram. As a precaution, we will still check that the angle of facet number 1 is above the critical angle of the gemstone to be cut.

57 + 16 girdle = 73 facets: Here we discover the number of facets of the future gemstone. The stone will have 57 facets + 16 around the girdle (if faceted), for a total of 73 facets.

8-fold, mirror-image symmetry: An 8-fold symmetry with a mirror effect was used to draw this cutting plan. In other words, you will only be interested in this function if you want to design cutting plans with software like GemCad, for example.

96 index: The diagram is designed to be cut with a 96-step indexed wheel. Note that the most common indexed wheels are: 64, 96, 120.

L/W = 1.000 T/W = 0.584 U/W = 0.584 P/W = 0.432 C/W = 0.111: These are measurement ratios where the letters mean: L = Length, W = Width, P = Pavilion, C = Crown, T/U = Table. You will understand that these ratios depend on the gemstone's width (W).

Vol/W^3 = 0.199: The volume-to-width-cubed ratio. An important ratio that allows you to calculate the estimated weight of your cut stone based on the estimated width.

diagramme_1.8

Here is what the second box gives us as information:

As you can see, it is composed of 2 parts, one called Pavilion and the other Crown. In general, in precision cutting, we start by cutting the pavilion, but it would also be possible to start with the table. The method used is the meeting point method.

This table should be seen as being composed of three columns:

A letter or number corresponding to the one indicated on the facets of the cutting plan, which serves as a guide.

An angle: this will be the angle at which the facets must be cut.

The indices that should be used on the indexed wheel.

To understand well, let’s take, for example, the third row of the pavilion:

1 | 41.5° | 96-12-24-36-48-60-72-84

Translating this row into English: number 1 indicates the corresponding facets on the cutting plan. They must be cut at an angle of 41.5° at the following indices on the indexed wheel: 96-12-24-36 etc.

If you understand this row, the rest of the cutting plan works on the same principle.

Note that row G1 represents the girdle (G = girdle in English), which will give the shape of the stone.

Thank you for reading this article and happy cutting.