Cut design of diamonds providing plenty of visual-perceptible reflection for ornamental use and observation method thereof

In a cut design of an ornamental diamond,

• a cut design providing plenty of visual-perceptible reflection, comprising:
• a substantially round or polygonal girdle having an upper horizontal section surrounded by an upper periphery and a lower horizontal section, parallel to the upper horizontal section, surrounded by a lower periphery;
• a crown of a nearly polygonal truncated pyramid formed upward above the upper horizontal section of the girdle having a regular octagonal table facet at the top of the polygonal truncated pyramid, eight crown main facets, eight star facets and sixteen upper girdle facets;
• and
• a pavilion of a nearly polygonal pyramid formed downward below the lower horizontal section of the girdle having eight pavilion main facets and sixteen lower girdle facets,
• wherein a center axis stands from a center apex of the pavilion polygonal pyramid through a center of the table facet;
• first planes each runs from the center axis through each of eight vertexes of the table facet;
• and second planes each runs from the center axis and divides an angle between the two neighboring first planes into two equal angles,
• wherein each of the crown main facets is a rectangular plane surface having two opposite vertexes, one being one of vertexes of the table facet and the other being a cross point of the upper periphery of the girdle with a first plane passing the vertex of the table facet,
• the rectangular plane surface having other two opposite vertexes each positioned on a neighboring second plane and coinciding with a vertex of a neighboring crown main facet;
• each of the star facets is a triangle having a base coinciding with a side of the table facet and a vertex coinciding with a coinciding vertex of two neighboring crown main facets each having a side passing each of the both ends of the base;
• each of the upper girdle facets is a triangle having a side coinciding with one of sides of a crown main facet and crossing the upper periphery of the girdle at an end of the side and a vertex at which a second plane passing the other end of the side crosses the upper periphery of the girdle;
• each of the pavilion main facets is a rectangular plane surface having two opposite vertexes, one being a cross point of a second plane with the lower periphery of the girdle and the other being at the center apex of the pavilion polygonal pyramid,
• the rectangular plane surface having other two opposite vertexes each positioned on a neighboring first plane, the pavilion main facets each having a side coinciding with a side of a neighboring pavilion main facet and two vertexes coinciding with two vertexes of the neighboring pavilion main facet;
• and
• each of the lower girdle facets is a triangle having a side coinciding with a side of one of the pavilion main facets and crossing the lower periphery of the girdle at an end of the side and a vertex at which the first plane passing the other end of the side crosses the lower periphery of the girdle,
• wherein a girdle height (h) between the upper and the lower horizontal sections of the girdle is 0.026 to 0.3 times a girdle radius;
• a pavilion angle (p) between the pavilion main facet and the lower horizontal section of the girdle ranges from 37.5 degrees to 41 degrees;
• and a crown angle (c) between the crown main facet and the upper horizontal section of the girdle is within a range of satisfying the following equations:
• c>−2.8667×p+134.233 and p<¼×{(sin−1(1/n)+sin−1(1/n·sin c))×180/π+180−2c},
• wherein
• n:
• refraction index of a diamond,
• π:
• circular constant,
• p:
• pavilion angle in degrees, and
• c:
• crown angle in degrees.

An observation method of an ornamental diamond, comprising:

• providing an ornamental diamond of a round brilliant cut which comprises a substantially round or polygonal girdle having an upper horizontal section and a lower horizontal section parallel to the upper horizontal section, a crown on the upper horizontal section of the girdle having a table facet and at least one crown main facet, and a pavilion below the lower horizontal section of the girdle having at least one pavilion main facet, wherein a girdle height (h) between the upper and the lower horizontal sections of the girdle is 0.026 to 0.3 times a girdle radius, a pavilion angle (p) between the pavilion main facet and the lower horizontal section of the girdle ranges from 37.5 degrees to 41 degrees, and a crown angle (c) between the crown main facet and the upper horizontal section of the girdle is within a range of satisfying the following equations:
• c>−2.8667×p+134.233 and p<¼×{(sin−1(1/n)+sin−1(1/n·sin c))×180/π+180−2c},
• wherein
• n:
• refraction index of a diamond,
• π:
• circular constant,
• p:
• pavilion angle in degrees, and
• c:
• crown angle in degrees and
• observing, above the table facet of the diamond, lights coming into the diamond through the table facet and crown facets including the crown main facets, star facets and crown girdle facets and emitted from the table facet and the crown facets with a sight line having an angle less than 20 degrees with a vertical line at the center of the table facet.