Up to now several methods are used to determine inclusions in diamonds, all of which have the disadvanta- ge that the inclusions are difficult to locate with respect to the outer surface of the diamond. Mostly two- dimensional images of the diamond will be obtained, what leads to an inaccurate location of such inclusion.

The invention has for its-object to avoid above- mentioned disadvantages, and the method according to the invention is distinguished in that said diamond is fixed on a holder, said diamond on the holder is observed under a predetermined angle to obtain an image, ! further a second measurement is carried out to obtain two data to be calculated in a computer in order to-localize the inclusion with respect to the outer surface of said diamond. According to a first embodiment of the invention the method is further distinguished in that, said diamond is fixed on a holder, said diamond on the holder-is detected under a predetermined angle to obtain a referen- ce image, further the direction of observation is at least changed one time, to obtain just as much as chan- ges, wherein the image-data are fed into a computer to calculate a tridimensional image including the or each inclusion with respect thereof.

Once the inclusion is clearly located with respect to the outer surface of the diamond, said diamond can easily be cut through the most optimal plane, calculated by the computer. This optimal plane leads through the inclusion, so when cutting the diamond the inclusion is disappeared.

Although the viewing direction with respect to the diamond can be carried out by repositioning the scanner

and so on, it is according to the invention easier to rotate and/or translate the holder with the diamond with respect to a fixed direction of observation.

Further it is one of the objectives of the invention to introduce a correction factor, related to the refrac- tive index of the diamond material to be taken up in the calculation when the scanning direction is deviating from a direction of observation, perpendicular to the diamond surface.

To easily create a correct location and/or largeness of the inclusion in the diamond, an optical cylinder will be used, the diameter and the detecting direction is used for the calculation by the computer.

According to a further embodiment the inclusion can be localized by using a scanner having focussing means to obtain a depth position along said direction of observa- tion by focusing said inclusion.

The invention will be elucidated by the following description of an embodiment to localize inclusions in the diamond.

In the drawing: Figure 1 is a perspective view of an scanning-embo- diment according to the invention for scanning a diamond upon a holder.

Figure 2 A, B, C, D, indicates the sequential steps of the preferred method according to the invention.

In figure 1 a housing 1 contains a holder 2, upon which a diamond D is fixed. By means of arbitrary and suitable motor means, it is possible to rotate the holder and/or to translate the holder, in order to position the diamond in an optical axis a, being the optical axis of a projecting light-beam 7, projected through the diamond unto a half permeable mirror, refuting in a diamond-image at a microscope and/or camera 3 and to a scanner 4.

When projecting the light it is possible to bring the holder 2 in the correct position with respect to the

microscope crosswires in a manual way carried out by an operator. The scanner 4 is used to obtain the data neces- sary for this particular image and to use this data in a calculation by a computer.

The several steps for carrying out the method accor- ding to the invention is explained in figure 2. a) Fix the diamond on the table, and take a scan 4 of the outer surface of the stone at an arbitrary initial position. The coordinates of this position are X0, Y0, Z0, α0, ß0, γ0. i) rotate the stone to make the necessary inclusion visible through the microscope- (with the measuring ocu- lar) b) Move the inclusion in front of the crosswire 9 of the microscope. The operator looking through the micro- scope does this by controlling the table. The translati- ons X1, Y., zu and rotations a1, ß1 81 the diamond on the table has performed, starting from its initial position, are registered. A facet is determined (its normal is ( α1, ß1, γ1), through which the inclusion is seen. A cy- linder (or line) is determined so that the inclusion is inside said cylinder (or is crossed by said line). The same procedure (steps a and b) is carried out from several different positions"n". c) Different positions are understood as either viewing through different facets of the diamond, or viewing through the same facets but from different direc- tions. The different set of translations and rotations are registered: X2...Xn, Y2...Yn, Z2...Zn, α2...αn, ß2...ßn, Y2... Yn' d) The position of the inclusions inside the diamond is calculated out from the registered translations and rotations, the scan of the outer surface and knowledge of the refractive index of the diamond. The position of an inclusion is determined as the nearest cross-centres of

the lines or cylinders created on step b. A symbol of the inclusion 8 is projected into the scan.

The invention is not limited to the method according to the lines above. For example the miroscope crosswire may be replaced by a"coordinate map", so avoiding a translation of the holder in each viewing direction.