Diamond graders draw a diagram of the inclusions in the diamond (left) to a diagram (right) to create a map of the diamond's inclusions, called the "plot." The plot will be used to help the diamond lab give the diamond its final grade on the clarity scale.
Diamond Grading Plot
A stone plot on a diamond grading report is a bit like a fingerprint. It records the significant internal and external characteristics of the diamond as a way to help positively identify that diamond and justify its clarity grade.
Traditionally plotting in the lab was done by freehand sketching on paper. Today, grading laboratories use computer programs that assist with creating the plot while at the same time putting it into digital form. AGSL has a unique, customized program that allows the grader to plot freehand so that the inclusions on the plot match how they appear in the stone. Using the AGSL proprietary software the grader can rotate the diagram 360 degrees and draw freehand the inclusions exactly as he or she sees them. They can be repositioned, deleted, morphed and scaled as needed until the plot represents the diamond exactly as it is. In addition, it expedites the grading process. Other laboratories use generic shapes to represent inclusions.
At AGSL, the facet diagram used to create the plot matches the facet arrangement of the diamond exactly. Most other grading laboratories use generic or approximate diagrams.
The inclusions are first observed in the loupe at 10x, then plotted from the microscope view at 10x (Figures 1 and 2, above).
The plot is not translational, (slides across the axis, like Figure 3) but reflective, so the #1 on the crown corresponds to the #1 on the pavilion, the #2 on the crown corresponds to the #2 on the pavilion, etc. It’s quite counter-intuitive, but the way plotting has traditionally been done. Just imagine taking the plot and folding it in half (Figure 4)
Figure 3. Translational plotting, where the #1 bezel main corresponds to the #1 pavilion main by "lifting up" the diamond crown and placing it over the pavilion. This is not how plots are oriented.
Determining which inclusions end up on the plot and which do not depend on the best representation of the stone, including factors such as the overall clarity of the stone, and the clarity grade of the inclusion itself. Ultimately, the most important considerations when plotting are the stone are ensuring the plot represents the clarity grade of the stone appropriately, and the stone can be identified based on its unique configuration of inclusions and blemishes.Rotation Plane
Figure 4. This is how plots are traditionally oriented. Note that the feather in bezel #1 also breaks through the girdle to the upper half on the left #1 lower half.