BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to gemstone observation, and more particularly to an apparatus and method for isolating and observing the fire of a gemstone.  
         [0002]     The quality and value of faceted gemstones are often described in terms of the “four C&#39;s”: carat weight, color, clarity and cut. Carat weight is the most objective, because it is measured directly on a balance. Color and clarity are factors for which grading standards have been established by the Gemological Institute of America (GIA), among others.  
         [0003]     Cut is much less tractable. Unlike color and clarity, for which a legacy of teaching, trading, and laboratory practice have created a general consensus, there are a number of different grading systems for grading cut of a gemstone. Inherent in most of these systems is the premise that there is one set, or a narrow range, of preferred proportions for some gemstones, and that any deviation from this set of proportions diminishes the appearance or attractiveness of the gemstone. However, under this premise, gemstone cutters typically apply these proportions only to obtain the largest possible size gemstone from an uncut stone, without specific regard to the stone&#39;s eventual appearance.  
         [0004]     Most gemstones are a convex polyhedron which can be specified according to a number of parameters.  FIG. 1  illustrates various parameters that define the proportions of one type of gemstone, a round brilliant cut (RBC) diamond. This type of gemstone can be specified according to eight parameters. Crown angle is the angle, in degrees, between the bezel facets and the girdle plane. Pavilion angle is the angle, in degrees, between the pavilion mains and the girdle plane. Table size represents the width of the table as a percent of the girdle diameter. Culet size represents the width of the culet as a percent of the girdle diameter. Star length is a ratio of the length of the star facets to the distance between the table edge and girdle edge. Lower girdle length represent a ratio of the length of the lower girdle facets to the distance between the center of the culet and the girdle edge. Girdle thickness is preferably measured between bezel and pavilion main facets, and is expressed as a percentage of girdle diameter. Finally, girdle facet number is the total number of facets on the girdle. Given a number of gemstones of the same color, weight and clarity, varying any of the above parameters produce different appearances.  
         [0005]     Other than color, weight, and clarity, gemstone appearance has historically been described chiefly in terms of three aspects: brilliance, scintillation, and fire. While interrelated, these aspects can be characterized independently. Brilliance, or brightness, generally refers to the level of white light returned through the crown of a gemstone to an observer overhead. Scintillation refers to flashes of light reflected from the crown of a gemstone, particularly as the gemstone is rotated or tilted. Fire is the result of the light-dispersive quality of a gemstone, and refers to visible rays or flares of colored light returned by the gemstone.  
         [0006]     It is believed that with knowledge about how cut relates to each of these aspects, alone or in combination, then perhaps improved cut parameters can be established to yield more attractive, and thus more valuable, gemstones. Unfortunately, each aspect above represents a complex concept without a precise mathematical definition, making it very difficult to measure on actual gemstones.  
         [0007]     Models have been developed for some aspects, however. For example, GIA developed a mathematical model for brilliance, discussed in  Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Brilliance , by Hemphill et al., Gems &amp; Gemology, Vol. 34, No. 3, pp. 158-183, the contents of which are incorporated by reference herein in their entirety and for all purposes. GIA&#39;s brilliance model uses a simulated round brilliant cut (RBC) diamond and a modeled light source of diffused, hemispherical white light shining on the crown. Then, researchers used computer simulation techniques to examine mathematically how millions of rays of light from the virtual light source interact with the virtual gemstone. This model generated images and a numerical measurement of the optical efficiencies of the gemstone called weighted light return (WLR). The WLR is a weighted sum of the amount of light returned through the crown of the virtual diamond to all positions of observation above the girdle. Thus, WLR approximates overall brilliance in an environment with even diffused lighting and no objects, such as an observer, in the environment.  
         [0008]     Similar assumptions and qualifications were used in developing a metric for fire. See  Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Fire, and More About Brilliance , Gems &amp; Gemology, Vol. 37, No. 3, pp. 174-197, the contents of which are also incorporated by reference herein for all purposes. While brilliance is emphasized with diffuse illumination found in most common lighting environments, fire is best observed using a highly directed, narrow beam of light, referred to herein as “spot lighting.” Accordingly, GIA chose to model the directed lighting as a bright point source of illumination located very far from the gemstone, i.e. at infinite distance, centered over and directed toward the gemstone&#39;s table. Under these conditions, the unpolarized light rays entering the crown facets are parallel to one another and perpendicular to the table, to illuminate the entire crown. The metric derived—dispersed colored light return, or DCLR—describes the potential of an RBC gemstone with certain proportions to display dispersed colored light when viewed face-up.  
         [0009]     Fire is the most difficult aspect of a gemstone to observe. Fire is often mixed with scintillation, the white light flashes that obscure the rays of colored light. Further, white light in general, either from the lighting environment itself or returned from the gemstone as brilliance, can overwhelm and suppress the visible effects of fire.  
         [0010]     A particular type of directed light source, for example one which approximates the GIA modeled light source, can isolate or enhance observable fire. However, several problems exist with finding and using such a source. Commercially-available narrow beam spot lights are not sufficiently directed, and allow too much white light from too many angles to reach a gemstone being observed, obscuring the fire. On the other hand, some highly directed light sources, such as lasers or light emitting diodes, radiate at too little of the visible spectrum for viewing the full range fire-based color separation. What is needed is a apparatus and method by which a white light source is channeled directly to a gemstone, in order to better isolate, observe and measure fire.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention is directed toward providing a light source which isolates and accentuates a gemstone&#39;s fire. This invention overcomes the limitations of conventional lighting schemes by providing directed, spot lighting having a full spectrum of visible radiant energy, which allows an observer to view the full extent of dispersion of light within a gemstone into separate wavelengths.  
         [0012]     In one exemplary embodiment of the invention, an apparatus for providing a spot lighting source for observing fire of a gemstone includes a tube. The tube has an inlet for receiving a portion of light from a light source, and an outlet for providing spot lighting from the received portion of light channeled through the tube. Accordingly, the spot lighting carries approximately the same spectrum as the original light source. The apparatus further includes a mask, coupled with the tube to shield the outlet from other portions of light from the light source.  
         [0013]     The another embodiment, a method of observing fire from a gemstone includes the steps of receiving a portion light from a visible or white light source at an inlet of a tube, and channeling the received portion of light through the tube. The method further includes the step of outputting the channeled light as spot lighting from an outlet of the tube. In the embodiment, the light channeled through the tube is directed but not diminished, so that the spot lighting has approximately the same spectrum as the light from the light source. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]      FIG. 1  illustrates various proportions of one type of gemstone.  
         [0015]      FIG. 2  is a perspective view of a system for providing a spot light source for observing fire of a gemstone.  
         [0016]      FIG. 3  is a cross-sectional view of a system for providing a spot light source from a portion of light from a light source to a gemstone. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     This invention relates to an apparatus and method for isolating colored light returned from within a gemstone. More specifically, this invention provides an apparatus and method for providing directed or spot lighting to a gemstone for observing the full effects of dispersion of a white light source by the gemstone into individual rays of colored light, known as “fire.” In a particular embodiment, this invention uses a conventional daylight-approximating light source and provides narrow spot lighting having the same or near-same spectral characteristics as the light source. Thus, this invention avoids the need for lenses, internal reflective layers for light propagation, or other mechanisms that modify or alter a light source.  
         [0018]      FIG. 2  shows an embodiment of an apparatus  200  for providing spot lighting to a gemstone. The apparatus  200  is generally adapted for use with any light source, but is preferably employed in combination with a daylight-approximating light source. As used herein, “daylight approximating” refers to a light source that approximates diffused, white light, or in other words, light which radiates all or nearly all of the visible electromagnetic radiation spectrum. The preferred operating environment for the apparatus  200  is dark other than the light source described herein.  
         [0019]     The apparatus includes a tube  202 . The tube includes an inlet  204  and an outlet  206  on an opposite end from the inlet  204 . The inlet  204  is configured to receive a portion of light  205  from a light source  209 , which received light is channeled through the tube  202  toward the outlet  206 . The portion of light  205  received at the inlet  204  can represent, for example, 1 to 5 degrees in arc-length of a cross-section of the radiation profile of light  205  emitted from the light source  209 . The apparatus  202  also includes a mask  208  coupled to the tube  202  to shield other portions of the light  205  from the tube  202  or outlet  206 .  
         [0020]     The tube  202  is preferably straight, elongate and hollow. In an alternative embodiment, the tube  202  may have a squared or angled cross-section along its circumference. The tube  202  is preferably 0.5 to 6 feet in length, and in a specific embodiment is 2 to 3 feet in length. The tube  202  may be any length, however, that sufficiently channels light without excessive loss. The interior diameter of the tube  202  is preferably between 0.1 and 1 inches. In one exemplary embodiment, the tube  202  has an inner diameter of approximately 0.5 inches. In yet another embodiment, the apparatus  200  can include, inside tube  202  or near the inlet  204  or outlet  206 , an aperture or an iris that is adjustably sized for different-sized gemstones.  
         [0021]     The tube  202  can be formed of metal, plastic or glass, or any other suitably rigid material, such as ceramic or polypropylene. The tube  202  is formed of a material having an inner polished surface that channels light with a particular amount of reflection, absorption, or dispersion, and preferably minimizing each. In one embodiment, the tube  202  includes an interior coating or layer that is selected for its particular light propagation qualities.  
         [0022]     In a preferred embodiment, the apparatus  200  is used in combination with a light source  209  that is a daylight-approximating halogen lamp, such as an MR16 halogen display lamp (12 Volt, 50 Watt, 4700 K color temperature and 10 degree narrow spot) manufactured by Solux™. The light source  209  can include a filter. While white light is preferred, it should be understood that other types of light-producing devices may suitably be used as the light source  209 .  
         [0023]     The mask  208  is preferably coupled to the tube  202  at or near the inlet  204 , but is generally positioned between the inlet  204  and the outlet  206 . In one embodiment of the invention, the mask  208  is shaped to correspond to the illumination profile or pattern of the light source  209 . For example, the mask  208  can be round and rigid like a plate. However, it should be readily apparent to one skilled in the art that the mask  208  can have any shape, and a wide range of sizes and rigidity. The mask  208  is also preferably planar and thin, but can have any thickness. The mask  208  can be formed of any rigid or semi-rigid, sufficiently opaque material or structure which can block the passage of light radiation emitted from the light source  209  or other extraneous sources of light in the lighting environment. In this regard, the exterior surface of the mask  208  and the outer surface of the tube  202  can be dark and non-reflective in a practical implementation to reduce the amount of potential light reflections. Additionally, the mask  208  should be resistant to any thermal radiation generated by the light source  209 .  
         [0024]     The apparatus  200  can also include a mounting mechanism  210  for mounting the tube  202  to a fixed object, and for positioning the tube  202  at a particular orientation or location. For instance, the mounting mechanism  210  can have one end configured to attach to a wall, or to mount to a table or other flat surface. The other end of the mounting mechanism  210  can be coupled to the tube  202 . The mounting mechanism  210  is used to align the inlet  204  of the tube  202  with the light source  209 , and/or align and adjust the height or position of the outlet  206  relative to a gemstone being observed. In another embodiment, the tube  202  is held stationary by the mounting mechanism  210 , and a gemstone being observed is positioned a suitable distance away from the outlet  206  of the tube. In accordance with one practical embodiment, the gemstone is held at least three feet away from the outlet  206 .  
         [0025]      FIG. 3  is a cross-sectional view of an apparatus  201  for providing spot lighting, employed in a system  300  for observing fire of a gemstone  100 . Along with the apparatus  201 , the system  300  also includes a stage  110  for supporting one or more gemstones  100  being observed. The stage  110  is shown supporting only one gemstone for simplicity, however the stage  110  may be configured to support two or more gemstones. The stage  110  is preferably non-reflective. In one embodiment, the stage  110  is configured for supporting the gemstone  100  in a table-up position to allow for the maximum amount of dispersed colored light to be returned through the crown.  
         [0026]     When gemstone  100  is near, i.e. directly under, the outlet  306  of the tube  302 , and the light source  309  is near, i.e. directly over, the inlet  304  of the tube  302 , a portion  303  of the light  305  emitted from the light source  309  is channeled through the interior  312  of the tube  302  in the direction indicated. The interior  312  is generally defined by a the cross-sectional inner area of the tube  302 , summed along the length of the tube. The portion  303  of the light  305  generally corresponds to the area of the inlet  304 , and includes visible radiation from any angle. The portion  303  of light  305  that is received at the inlet is channeled to the outlet  306 , where it is provided as a directed, spot lighting  307 . Importantly, very little to none of the visible spectrum of the received portion  303  of light is lost in the spot lighting  307 .  
         [0027]     A mask  308  shields an area around the gemstone from the light  305  of the light source  309 . The mask  308  may also be configured to shield the area from other light of the lighting environment, such as indirect sunlight, other overhead lights, etc. The mask  308  therefore prevents dispersed white light from reaching the gemstone  100  and obscuring the effects of fire from the spot lighting  307 .  
         [0028]     In one embodiment, the apparatus  201  is stationary, and the stage  110  and light source  309  are moved to their positions. In an alternative embodiment, the stage  110  and light source  309  are stationary, and a mounting mechanism  310  is configured for allowing the tube  302  to be placed into position. In still yet another embodiment, the light source  309 , the apparatus  201  and the stage  110  are all movable.  
         [0029]     The present invention may be specifically embodied as a tool to train observers to look for the specific colored flashes or rays of light that emanate from a gemstone as a result of its dispersive qualities. This invention may also be embodied as a system for measuring or characterizing the effects of fire. In a measuring system, a measuring device such as a colorimeter may be positioned near the gemstone to determine and/or quantify the specific colors of the gemstone&#39;s fire. Alternatively, a photodetector or similar instrument may be used to determine a level of colored light returned by a gemstone, or compared with the spot lighting supplied by the apparatus  100 . In this alternative embodiment, a filter or group of filters associated with the photodetector may be used to isolate specific wavelengths of visible colored light. A measuring system can also include a computer for processing measurement data, and a database for storing the results of the processing. Further, the database can be compiled as a reference, which can be accessed for later measurements and/or comparisons.  
         [0030]     By isolating and observing the effects of fire of many gemstones, it can be determined how a particular cut relates to this aspect of a gemstone&#39;s appearance, assuming other factors such as color, clarity and weight are the same. Thus, this invention provides useful information for establishing a set of preferred proportions for gemstones.  
         [0031]     While various embodiments of the invention are described above, it should be understood that they are presented for example only, and not as limitations to the following claims. Accordingly, the scope and breadth of the present invention should only be defined in accordance with the following claims and their equivalents.
An apparatus, system and method for providing spot lighting for observing a gemstone is presented. In particular, the spot lighting provided by the invention allows for observing of the fire of a gemstone, i.e. The visible effects of light dispersion into separate colors. The apparatus includes a tube for receiving a portion of a multi-spectral light source, and a mask coupled to the tube for blocking other portions of the light source. By selecting the proper tube dimensions and aligning the tube with both the light source at an inlet and a gemstone at an outlet, the spot lighting source provides direct lighting for isolating and accentuating the effects of fire.