This chart will help evaluate the amount of rough lost in trimming a stone (while maintaining its current design). I made this to help judge whether cutting out a certain fault is worth it in terms of lost carat weight. This also gives a measure of loss of yield if you dop inaccurately. The calculation is a trivial one - simply the cube of the final to original size ratio, but I never seem to have my calculator to hand.
Locate the current (or maximum possible) dimension of the stone across the top of the chart. This can be the length, width, or any linear scale of the stone. Scan down the column until you reach the entry corresponding to the final, corresponding dimension (for example, after cutting out that nasty veil). The table entry will give you the fraction of the current /maximum carat weight that will remain.
For example, I was working on a piece of tourmaline and managed to rough out a stone 6.5 mm wide. On careful examination, I found a veil just inside one of the girdle facets. Cutting away 0.5 mm would guarantee a flawless stone 5.5 mm wide (0.5 mm smaller on both sides!). The table indicates the resulting stone would weigh 61% of the original. It is also interesting (and depressing) to see how rapidly one loses carat weight if you dop a small (i.e. expensive) piece of rough inaccurately - for example, missing the ideal placement of that 5 mm sapphire by 1/4 mm will reduce your yield by almost 30%.
Starting Stone Size
|
10 |
9.5 |
9.0 |
8.5 |
8.0 |
7.5 |
7.0 |
6.5 |
6.0 |
5.5 |
5.0 |
4.5 |
4.0 |
3.5 |
3.0 |
2.5 |
2.0 |
1.5 |
1.0 |
|
|
0.50 |
0.0001 |
0.0001 |
0.0002 |
0.0002 |
0.0002 |
0.0003 |
0.0004 |
0.0005 |
0.0006 |
0.0008 |
0.0010 |
0.0014 |
0.0020 |
0.0029 |
0.0046 |
0.0080 |
0.016 |
0.037 |
0.13 |
|
1.0 |
0.0010 |
0.0012 |
0.0014 |
0.0016 |
0.0020 |
0.0024 |
0.0029 |
0.0036 |
0.0046 |
0.0060 |
0.0080 |
0.011 |
0.016 |
0.023 |
0.037 |
0.064 |
0.13 |
0.30 |
1.0 |
|
1.5 |
0.0034 |
0.0039 |
0.0046 |
0.0055 |
0.0066 |
0.0080 |
0.0098 |
0.012 |
0.016 |
0.020 |
0.027 |
0.037 |
0.053 |
0.079 |
0.13 |
0.22 |
0.42 |
1.0 |
|
|
2.0 |
0.0080 |
0.0093 |
0.011 |
0.013 |
0.016 |
0.019 |
0.023 |
0.029 |
0.037 |
0.048 |
0.064 |
0.088 |
0.13 |
0.19 |
0.30 |
0.51 |
1.0 |
||
|
2.5 |
0.016 |
0.018 |
0.021 |
0.025 |
0.031 |
0.037 |
0.046 |
0.057 |
0.072 |
0.094 |
0.13 |
0.17 |
0.24 |
0.36 |
0.58 |
1.0 |
|||
|
3.0 |
0.027 |
0.031 |
0.037 |
0.044 |
0.053 |
0.064 |
0.079 |
0.098 |
0.13 |
0.16 |
0.22 |
0.30 |
0.42 |
0.63 |
1.0 |
||||
|
3.5 |
0.043 |
0.050 |
0.059 |
0.070 |
0.084 |
0.10 |
0.13 |
0.16 |
0.20 |
0.26 |
0.34 |
0.47 |
0.67 |
1.0 |
|||||
|
4.0 |
0.064 |
0.075 |
0.088 |
0.10 |
0.13 |
0.15 |
0.19 |
0.23 |
0.30 |
0.38 |
0.51 |
0.70 |
1.0 |
||||||
|
4.5 |
0.091 |
0.11 |
0.13 |
0.15 |
0.18 |
0.22 |
0.27 |
0.33 |
0.42 |
0.55 |
0.73 |
1.0 |
|||||||
|
5.0 |
0.13 |
0.15 |
0.17 |
0.20 |
0.24 |
0.30 |
0.36 |
0.46 |
0.58 |
0.75 |
1.0 |
||||||||
|
5.5 |
0.17 |
0.19 |
0.23 |
0.27 |
0.32 |
0.39 |
0.49 |
0.61 |
0.77 |
1.0 |
|||||||||
|
6.0 |
0.22 |
0.25 |
0.30 |
0.35 |
0.42 |
0.51 |
0.63 |
0.79 |
1.0 |
||||||||||
|
6.5 |
0.27 |
0.32 |
0.38 |
0.45 |
0.54 |
0.65 |
0.80 |
1.0 |
|||||||||||
|
7.0 |
0.34 |
0.40 |
0.47 |
0.56 |
0.67 |
0.81 |
1.0 |
||||||||||||
|
7.5 |
0.42 |
0.49 |
0.58 |
0.69 |
0.82 |
1.0 |
|||||||||||||
|
8.0 |
0.51 |
0.60 |
0.70 |
0.83 |
1.0 |
||||||||||||||
|
8.5 |
0.61 |
0.72 |
0.84 |
1.0 |
|||||||||||||||
|
9.0 |
0.73 |
0.85 |
1.0 |
||||||||||||||||
|
9.5 |
0.86 |
1.0 |
|||||||||||||||||
|
10 |
1.0 |