How to Visually Measure the Depth Ratio of a Diamond Pavilion

Among all the ratio parameters, the pitch-to-depth ratio is the most accurate parameter using visual inspection, and the error of diamond graders generally does not exceed 1%. There are two methods for visually measuring the ratio of the pavilion to the depth, that is, the ratio of the stage to the shadow and the side view. 

1. Taiwan film comparison method Use a 10x magnifying glass to observe the size of the image formed by vertically observing the reflection of the table through the facet of the pavilion. Depth of the pavilion is inferred by determining the ratio of the pavilion depth based on the percentage of the image radius to the table radius. 

 The specific steps are: 

① Let the line of sight pass through the table vertically, adjust the bottom tip to the center of the table, and find the reflected image of the table; 

②Focus on the pavilion facet, first look for the black triangular reflection image of the star facet, and then look around all the black triangular images (black small bow tie), you can find a gray octagonal table image outline around the culet; 

③ According to the ratio of the image radius of the table to the radius of the table, determine the ratio of the pavilion to the depth. The deeper the diamond pavilion, the larger the table image. When the table image is small and only occupies near the culet and is not obvious, the booth-to-depth ratio is 40%. 

 When the pavilion-depth ratio is less than 39%, there will be light leakage, and the image of the tabletop will not be seen at all, and the edge of the tabletop will appear. The image of the girdle is called the "fisheye effect". 

When the pavilion depth ratio is greater than 49%, there will also be light leakage, and the entire range of the table will be in a dark shadow, which is called "black bottom effect" or "blocky stone". 

 2. Side view method 

Under a 10x magnifying glass, observe the round diamond from the side parallel to the girdle plane, and you can see two or one bright band formed by the girdle reflected by the pavilion facets. 

 The positions where the bright bands appear and the ratio (h1:h2) between them are related to the depth of the pavilion. Generally speaking, h2 does not change much, mainly based on the size of h1 to determine whether the diamond pavilion is too deep or too shallow. If the pavilion depth ratio is large, h1 is obvious, and the ratio of h1 to h2 is large; if the pavilion depth ratio is small, h1 is small; if the pavilion depth ratio is small, the first bright band disappears, and the fisheye phenomenon appears. 

 The two shaded bands are the image of the girdle, which are white bright bands in actual observation, h1 is the distance from the culet to the first bright band, and the size of h1 is related to the ratio of pavilion depth (pavilion angle) 

 When the pavilion-depth ratio (pavilion angle) of round diamonds is large (such as 46%), h1 is obvious, and the ratio of h1 to h2 is also large 

 The pavilion depth of round diamonds is relatively small (such as 41%), the first bright band is not obvious, it is often on the culet, and h1 is also very small 

When the pavilion-depth ratio of round diamonds is smaller (less than 40%), the first bright band disappears, which usually indicates that the "fish-eye" phenomenon will appear