Abstract: An information mark invisible to the naked eye is applied to the polished facet of a diamond gemstone by coating the diamond gemstone surface with an electrically conductive layer so as to prevent the diamond becoming charged, forming the mark with a focused ion beam, and cleaning the diamond surface with a powerful oxidizing agent to reveal a mark having an appropriate depth, which does not detrimentally affect the clarity or color grade of the diamond.

Abstract: An invisible information mark is provided on a facet of a diamond gemstone by applying a plasma resist to the exposed surface of the gemstone, applying an electrically conducting layer of metal to the region where the information mark is to be formed, ablating a selected zone of the metal and resist layers by ultraviolet laser thus forming a mask on the surface of the facet, electrically connecting the metal layer and plasma etching the facet through the mask, thus forming a mark of appropriate depth on the surface of the gemstone.

Abstract: In order to test whether a diamond has had a layer a synthetic diamond deposited thereon, the diamond is radiated with ultraviolet radiation so as to form a pattern of beams of refracted and reflected radiation, the pattern of refracted and reflected radiation being observed on a screen behind the diamond.

Abstract: In order to produce on the table of a diamond gemstone (7), an information mark which is invisible to the naked eye using a ×10 loupe, an ultraviolet laser (1) having a wavelength of 193 nm is used in association with a mask (2) to irradiate the surface of the stone (7) at a fluence of less than 2 J/cm2 per pulse and with not fewer than 100 pulses, in the presence of air which reacts with the diamond (7) and causes the mark to be formed without any darkening which is visible when viewing using a microscope.

Abstract: In order to test whether a diamond has had a layer of synthetic diamond deposited thereon, it is irradiated with high energy ultraviolet radiation to cause emission of luminescence, the luminescence intensity produced by different zones of the diamond being measured and compared. In one embodiment an integrating enclosure (15) is used and the diamond (13) is mounted on a rotatable mount (14).

Abstract: In order to test whether a diamond has had a layer of synthetic diamond material deposited thereon, infrared radiation including radiation of wavelength substantially 7 .mu.m to 25 .mu.m preferably 7 .mu.m to 10 .mu.m emitted or transmitted by the diamond is observed, to detect differences between the compositions of different zones of the diamond.

Abstract: In order to test whether a diamond has had a layer of synthetic diamond deposited thereon, the surface area of the natural part of the stone is measured by measuring the radiant-flux density of radiation substantially of wavelength 230 nm to 320 nm in an integrating sphere containing the diamond. This is compared to the total surface area of the diamond.

Abstract: In order to examine a gemstone, the stone is irradiated and observed though a filter (5) at a first wavelength which is characteristic of a first class of gemstones. The filter can be rocked from a setting normal to the optical axis to transmit radiation of at least one reference wavelength. The intensities of radiation transmitted at first and reference wavelengths are observed and compared, to classify the gemstone as belonging to the first class or not. In order to detect whether the gemstone is a diamond or diamond simulant, the first wavelength comprises raman emission characteristic of diamond. In order to detect whether the gemstone is definitely natural or not definitely natural, the gemstone is classified as definitely natural if there is a maximum of absorption of radiation at 415.5 nm.

Abstract: In order to test whether a diamond 2 comprises synthetic diamond material, a plurality of different zones of the diamond 2 are irradiated with radiation substantially of wavelength substantially 230 nm to 320 nm, an image or reading of the radiation transmitted by each zone of the diamond 2 being produced.

Abstract: In order to provide a simple, safe and compact apparatus for distinguishing natural, colorless, or near-colorless diamond from synthetic diamond, the apparatus is equipped with a chamber in which a flash lamp irradiates a stationary diamond with irradiation which has a substantial component of ultra-violet light below 250 nm or 255 nm. The intensity of phosphorescence emitted by the diamond after irradiation by the lamp is measured by a photomultiplier tube which sends a signal to a microprocessor. There is a visual display of the elapsed time for the phosphorescence intensity to decrease to a threshold value. The diamond is classified as probably natural if it has no phosphorescence or a short phosphorescence time.

Abstract: For blocking or polishing a natural or synthetic stone having a Mohs hardness greater than about 5, a blocking head has a body, a mounting member which can move vertically with respect to the body, and a rotary spindle driven by a motor. The mounting member is carried by a leaf spring whose position is altered by a parallel linkage whose arm is driven by a motor. In this way, the spring can for soft landing apply an upwards bias opposing the gravitational force of the mass of the mounting member. When the stone is in contact with the scaife, the deflection of the spring measures the force on the stone, and this deflection is detected by an LVDT. Subsequently, the spring can apply a downwards bias to augment the working force. A microprocessor is responsive to the output of the LVDT and controls the motor so that the force applied to the stone complies with a predetermined program.

Abstract: This invention relates to a method and apparatus for classifying or sorting objects by projecting and irradiating an object through an irradiation zone and then examining the radiation emitted by the object to determine its class, the irradiating zone having a length in a vertical plane greater than its width where its length to width ratio is greater than 5:1.

Abstract: In order to provide secure and simple detection of diamonds when prospecting, a rock sample is reduced to powder particles which are automatically checked to see if they contain diamond particles (30) by processing an image of X-radiation transmitted through a layer of the particles. The image may be processed by comparing it with a further image of visible light transmitted by the layer of particles.

Abstract: In order to examine an object with radiation and measure the intensity of radiation used to illuminate the object, radiation is directed onto a wavelength selective mirror (31). In a first position, the mirror (31) reflects the illuminating radiation to a beam splitter (30) which passes the radiation to a detector (34). In a second position the mirror (31) directs the radiation to an object (33), radiation of the selected wavelength emanating from the object being reflected by the mirror via beam splitter (30) to the detector (34). The mirror (31) is rotated between the first and second position. In order to classify a diamond as natural or synthetic, a first signal is derived dependent upon the intensity of ultra-violet radiation transmitted by the diamond at 254 nm, and a second signal is derived dependent upon the intensity of radiation transmitted by the diamond at 365 nm and the diamond is classified as being definitely natural if the first signal is substantially greater than the second signal.

Abstract: In order to sort ore from associated mineral material, a method and apparatus of classifying an object is provided, the method including feeding the object along a feed path, irradiating the object with infra-red radiation of a first wavelength, the radiation of the first wavelength being focussed onto an irradiation zone intersecting the feed path, the irradiation zone having a length in the vertical plane substantially greater than its width in the vertical plane. The intensity of radiation emitted by the object at at least one second wavelength different from the first wavelength is examined, the second wavelength being characteristic of a first class of object or the ore to be sorted from the mineral, whereby the classification of the object may be derived.

Abstract: An apparatus and method to control the velocity and spacing of a spaced feed of objects, includes a member rotatable about an axis and having at least one receptacle, the objects being fed into the apparatus in spaced succession so that they are captured in the receptacle and so that they acquire the circular motion of the member. The receptacle has means for releasing the objects so that they are projected with a predetermined velocity and with a predetermined frequency. The phase relationship of a rotatable feeder and the rotatable member is controlled by generating a signal representative of the phase difference of the rotatable members, filtering the signal for maintaining loop stability and controlling the drive means of the rotatable member using the signal.

Abstract: Apparatus for optical inspection of particulate material such as diamond abrasive comprises a body (1), an open sample container (25) which can rise and fall in the body, a reference member (71) above the container, mounted in a removable compaction head (9) of which the height relative to the body is fixed, and an optical inspection head (11) mountable on the body in place of composition head. The container is raised into contact with the reference member so that the surface of the sample is levelled and placed at a predetermined height. The compaction head is then removed and replaced by the optical inspection head. Consequently, the sample surface is always presented to the optical inspection head in a predetermined relationship and in particular at a predetermined height.

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.