Abstract:
A gem identifying device using filtered transmitted light for use in distinguishing type-I colorless diamonds from type II colorless diamonds, and natural diamonds and gems from synthetic or treated diamonds and gems.

Description:
[0001]    This application is a Continuation of U.S. patent application Ser. No. 09/262,762, filed on Jul. 28, 1999, and incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The identification of natural, synthetic, and laboratory-treated gemstones presents an ongoing challenge to gemologists and jewelers. To address this problem, practical instruments are needed that will enable gemstones to be distinguished from one another quickly and easily.  
           [0003]    Gemologists have traditionally used the visible spectra of gemstones to help in their identification. When light passes through a gemstone, a portion of the visible spectrum of a gemstone may be observed by means of the spectroscope enabling a viewer, to see the pattern of sharp absorption lines and broad regions of absorption and transmission that are often characteristic of a particular gem material.  
         SUMMARY OF THE INVENTION  
         [0004]    This invention uses a selective filter to distinguish two different gemstones that may be similar in color, but differ in their visible spectra. One embodiment of the invention comprises:  
           [0005]    a) a light source;  
           [0006]    b) a glass plate on which the gemstone is placed for observation;  
           [0007]    c) an iris diaphragm to restrict light from being transmitted around the edge of the gemstone being examined;  
           [0008]    d) a selective filter, chosen depending upon the spectra of the two gemstones to be distinguished;  
           [0009]    e) and a lens to view the gemstone in transmitted light.  
           [0010]    By means of this invention, and the proper selection of the filter, it is possible to directly observe whether or not a gemstone is transmitting the light passed by the filter. By proper selection of the filter, one gemstone will appear to transmit the light, and it will appear bright, while the other gemstone will not transmit the light, and it will appear dark. The idea of gem identification by using filtered transmitted light is one novel aspect of the invention. The apparatus also provides for a convenient and expedient gem identification process.  
           [0011]    There are several possible applications of this invention. Specific applications include distinguishing:  
           [0012]    a) type-I a colorless diamonds which occur in nature from type-ii-a colorless diamonds (which are rare in nature and can be produced in the laboratory). For this application, the invention will make use of a bandpass filter with a center frequency of about 415 nanometers. The type I-a colorless diamonds will transmit this light and thus appear bright in the viewfinder. In contrast, a type II a colorless diamond will appear dark. Such a test will allow jewelers to quickly determine whether further evaluation for synthetic diamond material is required;  
           [0013]    b) diamonds that have been treated with a high refractive index glass to hide the visibility of surface-reaching fractures from non-treated diamonds. Diamonds that have been treated with a high refractive index glass have an altered absorption pattern compared to untreated diamonds. The transmission based gem detection system described herein deploys a band-pass filter which selects for high refractive index glass;  
           [0014]    c) colorless diamond from colorless synthetic mossanite (silicon carbide—a new diamond imitation material). For this application, this instrument deploys a filter which filters out light at wavelengths above about 430 nanometers. Diamond is relatively transparent in this region below 430 nanometers, while moissanite is more opaque and light absorbing for this region. Thus, when the selective filter permits illumination of the gem only with light below 430 nanometers, the diamond appears bright through the viewer. The moissanite appears dark under the same circumstances.  
           [0015]    d) natural color gemstones from laboratory-treated colored gemstones and from synthetic colored gemstones.  
           [0016]    No other similar gem-testing instruments are known. There are several colored lenses that are sold by Hanneman Gemological Institute of Castro Valley, Calif. that distinguish certain types of colored gemstones based upon how the gemstones appear in reflected white light when viewed through the lens. For example, such lenses may be used to separate topaz from aquamarine gems. There is also a device, known as a phosphorescope used for visual observation, and an instrument used for measurement of differences in transparency of gemstones to short-wave ultraviolet radiation. However, none of these products work on the basis of the same principle as the instrument described herein. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a schematic, exploded view of one embodiment of the gem identification viewer.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    In a preferred embodiment, shown in FIG. 1, the gem identification viewer comprises a viewing lens  10  which is aligned with filter  20  to form a filter assembly. The viewing lens  10 , which is preferably a magnification lens, is separated from the filter  20  by a spacer  30 . The filter assembly is deposited in eyepiece  40  and a top ring  15  is placed over lens  10  to further secure the filter assembly within the eyepiece  40 . The eyepiece  40  has a distal end  45  which is aligned within housing  50  through the top of said housing. Housing  50  may comprise a hollow tube with a generally spherical cross-section. Housing  50  contains side opening  55  to permit placement of the gem on the transparent observation plate  60 . The eyepiece  40  is secured within housing  50  by virtue of a ball plunger  65 . The bottom of housing  50  is aligned with iris diaphragm  70  which contains an iris opening such that light transmitted into the housing  50  from its distal end is restricted in a way that does not allow light to be transmitted around the edge of the gemstone to be examined. Optionally, the iris opening is adjustable. The iris diaphragm is aligned with first and second condenser lenses  80   a  and  80   b  which are oriented so as to condense light entering into the housing from the bottom opening. The diaphragm  70  and the first condenser lens  80   a  are separated by spacer  85   a  so as to protect the edge of the lens. The first and second lenses are similarly separated by spacer  85   b . The second condenser lens  80   b  is secured by bottom ring  90 . Bottom ring  90  is preferably a tubular ring shape which has the inner diameter of a handheld flashlight.  
         [0019]    According to a preferred method of gem identification, the user places a flashlight or other light source underneath the bottom ring  90  of the gem identification viewer so that light is transmitted up through the condenser lenses  80   a  and  80   b , through the iris diaphragm  70  and through the viewing platform  60 . A gem is placed on the viewing platform  60  and, while viewing through the viewing lens  10 , the iris diaphragm  70  is adjusted so that little or no light is transmitted to the viewing lens  10  from outside the edge of the gem. This represents a significant advantage over reflected light observation. The viewer then notes the brightness of the gem. By proper selection of the filter, one gemstone will appear to transmit the light and it will appear bright, while the other gemstone will not transmit the light and it will appear dark. The amount of light that is passed through both the gem and the filter  20  thereby permits ready visual identification of gem type and gem authenticity as given above. For example, colorless synthetic moissanite, a new diamond imitation material, may be distinguished from natural diamond by a jeweler using the described method with a low pass filter having about a 430 nanometer cutoff.  
         [0020]    In alternate embodiments, the location of the filter may be distal to the housing  50  relative to viewing lensl 0 . That is to say, the light may be filtered prior to transmission through the gem. Alternatively, the invention may deploy a monochromatic source at the critical wavelength either with or without a filter. The source should be portable, however, and thus sources requiring large power supplies are disfavored. Other embodiments may employ a light polarizing prism in place of the filter. By polarizing the source light before it reaches the gem, the transmitted light will be similarly polarized. Thus, a polarizing optical element placed in front of the lens can preferentially select out radiation transmitted with the same polarization. This may be used to distinguish gems based on their effect of polar qualities of light, or simply to act as a polar filter for filtering out non-critical wave length light while letting pre-polarized source light to be identified by a pre-lens polar optical element. The same principles may be employed using phase modulated light to distinguish gems. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody all warranted changes which reasonably come within the scope of their contribution to the art.