Abstract: In order to sort diamond-bearing ore particles conveyed on a wide belt, exciting radiation strikes the belt along an extended line. Diamonds are detected by passing the emitted radiation through a narrow band pass filter and sensing the Raman radiation with a photo-multiplier tube. Only axial-parallel rays passing through the filter reach the photo-multiplier tube. An array of side-by-side converging lenses can be used, the lenses being of rectangular shape as seen looking along the optical axis with their long axes at right angles to the line of radiation. The ore particles are in the plane of the foci of the lenses, so that radiation emitted by each particle is passed in parallel rays through the filter. In order to stop rays having an angle of incidence greater than the maximum permitted, to avoid identifying non-diamond material as diamond, a further converging lens is used to focus the rays at the plane of a telecentric stop. The stop stops rays having too great an angle of incidence.

Abstract: To make an elongate cut (1) in a diamond (2) using a laser radiation, a cylindrical optical system (5, 6) is used which converges the radiation at a greater angle of convergence in the plane of the cut (1) than in the transverse plane. In this way, the focal spot energy density is increased and cutting at depth is made more effective.

Abstract: In order to sort diamond-bearing ore particles conveyed on a wide belt, exciting radiation strikes the belt along an extended line. Diamonds are detected by passing the emitted radiation through a narrow band pass filter and sensing the Raman radiation with a photo-multiplier tube. Only axial-parallel rays passing through the filter reach the photo-multiplier tube. An array of side-by-side converging lenses can be used, the lenses being of rectangular shape as seen looking along the optical axis with their long axes at right angles to the line of radiation. The ore particles are in the plane of the foci of the lenses, so that radiation emitted by each particle is passed in parallel rays through the filter. In order to stop rays having an angle of incidence greater than the maximum permitted, to avoid identifying non-diamond material as diamond, a further converging lens is used to focus the rays at the plane of a telecentric stop. The stop stops rays having too great an angle of incidence.

Abstract: To weigh objects in quick succession, the objects are projected with a known horizontal velocity onto a ramp which has a surface which curves down through 90.degree.. The ramp can move horizontally in response to the impulse corresponding to the change in horizontal momentum of the object. A transducer senses the movement of the ramp and the output horizontal velocity of the object is sensed, enabling the change in horizontal velocity to be calculated. The mass of the object is calculated from the horizontal movement of the ramp and the change in horizontal velocity of the object. In order to obtain accurate sensing of the movement of the ramp, the transducer is a linear variable differential transformer having a primary winding energized by a cyclical carrier signal and two matched secondary windings in series; the secondary winding output signal is rectified to a corresponding DC voltage having ripple components, and a sample is taken of the signal at the zero voltage of the principal ripple component.

Abstract: To weigh objects in quick succession, the objects are projected with a known horizontal velocity onto a ramp which has a surface which curves down through 90.degree.. The ramp can move horizontally in response to the impulse corresponding to the change in horizontal momentum of the object. A transducer senses the movement of the ramp and the output horizontal velocity of the object is sensed, enabling the change in horizontal velocity to be calculated. The mass of the object is calculated from the horizontal movement of the ramp and the change in horizontal velocity of the object. In order to obtain accurate sensing of the movement of the ramp, the transducer is a linear variable differential transformer having a primary winding energized by a cyclical carrier signal and two matched secondary windings in series; the secondary winding output signal is rectified to a corresponding DC voltage having ripple components, and a sample is taken of the signal at the zero voltage of the principal ripple component.

Abstract: In order to color sort objects such as peas or sweets, they are dropped in succession through two integrating spheres. In the first sphere, the object absorbs infra-red radiation and the peak reduction in infra-red flux is detected in order to provide a signal responsive to the size of the object. In the second sphere, the object is illuminated with white light and the peak reduction in flux is detected by at least three detectors for three colors determined by filters. To make the illumination more uniform in the sphere, there is a step around the sphere almost half way down, with light sources equi-spaced around the step. The size signal is divided into the respective color signal in a micro-processor to produce a size-corrected color signal.

Abstract: Method and apparatus for examining a gemstone to determine a parameter thereof. A thin beam of light is projected onto the stone, the beam is moved relative to the stone, the position where the beam strikes the stone is sensed in a direction different from that in which the beam is projected, and a parameter is determined making use of information derived from such sensing.

Abstract: The color of gemstones or the like is assessed by projecting light onto the stone, using an interrupting member to regularly interrupt the path of the light shortly before it reaches the stone, the member having a normally white, diffusing interrupting surface, and using a detector for detecting the color of the light coming from the gemstone and from the interrupting surface of the interrupting member. Preferably, the stone is mounted in a chamber having normally white, diffusing internal walls and the diffusing interrupting surface is within the chamber.

Abstract: A rough gem stone is centered by mounting the stone on a dop, providing an image of the stone, as seen normal to the axis, providing a reference shape which corresponds to the shape of a cut stone, and superimposing the stone image and the reference shape, altering the size of one relative to the other until the reference shape corresponds to the stone that can be cut from the rough stone, and altering the position of the rough stone until the stone image registers correctly with the reference shape. In a method of working the stone, the final radial dimension to which the stone is to be worked is estimated and is used for terminating working when the actual radial dimension reaches the corresponding value.