Abstract:
A gemstone cut with a table facet, where the gemstone receives existing light from around the viewer and the facets on the bottom of the diamond effectively reflect the existing light back into the eyes of the beholder in such a manner as to maximize light performance, and to produce a unique and distinct look of light in the form of a Maltese cross under the table facet which can be observed in natural ambient light.

Description:
FIELD OF THE INVENTION 
     The invention relates to gemstones, preferably diamonds, that have a cut or shape that causes light entering the gemstone to exit in a specific optical pattern. In particular the present invention relates to diamonds where the light exiting through the table facet provides a pattern in the shape of a Maltese Cross. 
     BACKGROUND OF THE INVENTION 
     One of the values of gemstones, is in their appearance. The appearance of the gemstone can often be enhanced by cutting the gemstone into different shapes, and polishing the surface of the gemstone. This is especially true with gemstones that at least pass some light through them, especially diamonds. Depending on the angle that the light strikes the surface and the material of the gemstone, the light can neither be reflected from the surface or pass through the surface. If the light passes into the gemstone, it passes through the gemstone until it reaches another surface. At this other surface, the light in the gemstone can either be reflected back into the gemstone or pass out of the gemstone. 
     It is often desirable to shape the gemstone so that the light entering one area of the gemstone is redirected by the gemstone to exit from another area. In particular it is often desirable to maximize the light exiting one area, since this gives the gemstone a brilliance or sparkle. Many different gemstone cuts are known, particularly for diamonds, to try to maximize the amount of light that exits one particular area of the gemstone. 
     One of the most popular cuts for a diamond is known as the “brilliant”, which arranges the individual flat surfaces or facets to maximize the light passing out through the main table facet. The “brilliant” cut has a crown portion, a girdle portion and a pavilion portion. Each of these portions has a plurality of facets, especially the crown portion and pavilion portion. The arrangement of these facets is well known to a person of ordinary skill in the art of the present invention, and therefore no further description of the arrangement of facets in the “brilliant” cut is necessary or warranted. 
     There are many variations of the “brilliant” cut style. Very often the angle of the facets is changed slightly to account for the original shape of the rough diamond, to increase the yield from the rough diamond, or personal preferences. Sometimes the shapes of the facets are changed to provide a finish diamond with a square or rectangular shape. Even with these variations, the cuts still follow the well-known “brilliant” style. 
     There are many other antique facet designs, such as the “Old Mine Cut”. The arrangement of the facets in these antique designs are well known to a person of ordinary skill in the art of the present invention, and therefore no further description of the arrangement of facets in these antique facet designs is necessary or warranted. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a gemstone cut with a table facet, where the gemstone receives existing light from around the viewer and for the facets on the bottom of the diamond to effectively reflect the existing light back into the eyes of the beholder in such a manner as to maximize light performance, and to produce a unique and distinct look of light in the form of a Maltese cross under the table facet which can be observed in natural ambient light. 
     The present invention accomplishes this object in a polygonal gemstone with a girdle portion having corners and a girdle plane. A crown portion extends from one side of the girdle portion, and includes a table facet with a plurality of crown facets arranged around the table facet. A pavilion portion extends from another side of the girdle portion diametrically opposite the crown portion, and includes a plurality of pavilion facets tapering the pavilion portion together as the pavilion portion extends away from the girdle. The facets are in an arrangement or a facet structure that follows that of the antique facet design, the “Old Mine Cut” or the brilliant facet style, and where the angles of the facets have been proportioned in such a manner as to provide the above described Maltese cross effect under the table facet. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a side view of an embodiment of the gemstone cut; 
         FIG. 2  is a top view of the gemstone cut; 
         FIG. 3  is a bottom view of the gemstone cut; 
         FIG. 4  is a top view of the gemstone cut showing the Maltese cross pattern in a schematic view; 
         FIGS. 5 and 6  are top and bottom views respectively of one embodiment of the present invention; 
         FIGS. 7 and 8  are top and bottom views respectively of another embodiment of the present invention; 
         FIGS. 9 and 10  are top and bottom views respectively of still another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  shows a side view of a gemstone, not necessarily drawn to scale. The gemstone has a girdle portion  10  in a square or rectangular shape and having rounded corners  18 ,  FIG. 2 . The length to width ratios for rectangular stones are preferably less than 1.10:1. A crown portion  12  extends from one side of the girdle portion  10 , and a pavilion portion  14  extends from another side of the girdle portion  10 . The crown portion  12  and pavilion portion  14  are on diametrically opposite sides of the girdle portion  10 . The crown portion  12  and the pavilion portion  14  have a plurality of facets. The girdle portion  10  can optionally be smooth or faceted. 
     The crown facets include, a table facet  16 , four crown main facets  20 , and four crown corner facets  22 . Each of the four crown corner facets  22  is arranged in the area of one of the four rounded corners  18  of the girdle portion  10 . The crown main facets  20  and crown corner facets  22  are alternately arranged around the table facet  16  with each of the crown main facets  20  being arranged between two of the crown corner facets  22 . 
     The crown facets also include eight crown star facets  24  arranged between the table facet  16 , the crown main facets  20 , and the crown corner facets  22 . One of these crown star facets  24  is arranged between, and is adjacent, each adjacent pair of corner crown facets  22  and corner main facets  20 . Each crown star facet  24  is also adjacent to one edge of the table facet  16 . 
     The crown facets also include sixteen crown half facets or crown girdle facets  26  arranged around the table facet  16  and directly adjacent to the girdle portion  10 . Two of these crown half facets  26  are arranged between each adjacent pair of crown corner facets  22  and crown main facets  20 . Each of these crown half facets  26  is also directly adjacent to either a crown main facet  20  or a crown corner facet  22 . 
     The pavilion facets include four pavilion main facets  28  and four pavilion corner facets  30 . Each of the four pavilion corner facets  30  is arranged in the area of one of the four rounded corners  18  of the girdle portion  10 . The pavilion main facets  28  and pavilion corner facets  30  are alternately arranged around the pavilion portion  14  with each of the pavilion main facets  28  being arranged between two of the pavilion corner facets  30 . 
     The pavilion facets also include sixteen pavilion half facets or pavilion girdle facets  32  arranged around the pavilion portion  14  and directly adjacent to the girdle portion  10 . Two of these pavilion half facets  32  are arranged between each adjacent pair of pavilion main facets  28  and pavilion corner facets  30 . Each of these pavilion half facets  32  is also directly adjacent to either a pavilion main facet  28  or a pavilion corner facet  30 . The pavilion portion  14  can also have a culet  34 . 
     In order to produce the optical pattern of a Maltese cross  36 , as shown in  FIG. 4 , under the table facet  16 , the crown and pavilion facets are arranged in specific angular ranges with respect to a plane of the girdle portion  10 . These angles depend on the refractive index of the gemstone. For a diamond gemstone, the facets would be preferably arranged in the following ranges: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 crown main facets 20 
                 38-42 degrees 
               
               
                   
                 crown corner facets 22 
                 37-42 degrees 
               
               
                   
                 crown star facets 24 
                 28-35.5 degrees (FIG. 7 for  
               
               
                   
                   
                 example of upper limit) 
               
               
                   
                 crown half facets 26 
                 47-52.1 degrees (FIG. 5 for  
               
               
                   
                   
                 example of upper limit) 
               
               
                   
                 pavilion main facets 28 
                 40-41 degrees, preferably  
               
               
                   
                   
                 40.4-40.9 degrees 
               
               
                   
                 pavilion corner facets 30  
                 37-40 degrees 
               
               
                   
                 pavilion half facets 32 
                 42-45 degrees. 
               
               
                   
                   
               
             
          
         
       
     
     To further produce the optical pattern of a Maltese cross, it is preferable for the table facet to be 48-52% of the width of the diamond, the lower half facet length to be 50%+/−5% with respect to length from the edge of the girdle to the cullet, and the star facet/upper half facet ratio to be 45%-55% (+/−5%) with respect to table edge-to-girdle length. 
     The pavilion facets on the bottom of a diamond will function as either mirrors (reflectors of light, good) or windows (leakers of light, bad). An important step in the optical design is ensuring that the pavilion (bottom facets) are effectively reflecting light back to the viewer. Another important step in the optical design is ensuring that the crown of the diamond draws in its reflections from the brightest resources in the environment. The present invention is designed for the majority of its reflections from the 45-75° angular spectrum. 
     Several of the preferred embodiments of the gemstone in diamond are shown in  FIGS. 5 &amp; 6 ,  7  &amp;  8 , and  9  &amp;  10 . In  FIGS. 5 and 6 , the slope angles are shown for each facet. In  FIGS. 7 through 10 , the top angular measurement shown in each facet is the slope angle, and the bottom angular measurement is the index angle. The index angle shows the position of the facet around the stone. These actual angles can vary by approximately plus or minus one degree in these embodiments. The dimensions of the table facet and the culet are also shown. All of the facets in each type of facet can either have the same slope angle, or a slightly different slope angle as shown in the drawings. 
     An example of a gemstone cut according to the present invention is shown in the appendix. 
     The gemstone cut shape of the present invention is not limited to only the above described facets. Additional facets can be included, especially to complete an enclosed volume. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.