Procedure
Suitable stones
Diamonds are without doubt the most suitable stones, as they are the most resistant to the pressure of metal. Rubies and sapphires do not create great problems, as long as they are of a certain purity and have been cut as regularly as possible. The most delicate stones for this procedure are cubic zirconia, garnets, tourmaline, etc.
Suitable cuts
Square or princess cut is without doubt the most widely used and suitable for invisible setting, although rectangular and hexagonal shapes may also be used.
For the choice of cut it is important that when a group of stones are placed side by side there are no empty spaces between them, in such a way that the metal is not visible below the stones.
Preparation of the stones
1. To make stones more resistant to breakage caused by pressure of the metal, acute angles must be dealt with in the various ways indicated below.
2. To be able to set stones invisibly, a small groove must be effected under the girth of the stone. This cut requires noteworthy experience and the use of a special machine such as the one below.
Stone grooving machine for diamonds and coloured stones in a wide range of shapes, such as princess, baguette, hexagon and others. Presented by Gesswein USA
These are the various systems and criteria for cutting a groove under the girth of the stone:
Cross section of a support net with stones
Preparing a suitable prototype
There are different methods for preparing the model.
1. Modelling in wax:
to create the model by hand with simple bench equipment, requires a high degree of dexterity and precision, for those who do not have the chance to use rapid prototyping (CAD/CAM).
2. Direct modelling in metal:
this methods is above all suitable for models with extremely geometrical shapes. A lathe or milling machine can be used to help. The support net for stones can be made with the aid of a milling machine or directly with plate and wire.
3. Rapidprototyping:
the various systems are described and illustrated in the book "The Santa Fe Symposium" by Mr. Bud Krahn, page 447, 1998 edition. Due to their high degree of precision, these are without doubt the most suitable systems, although unfortunately they have high lnvestment costs.
The most delicate part of the model is the support net for the stones, which must be created with specific criteria illustrated in the drawings below.
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