From the handbook
The quality of the crystal is judged on a scale of 1 to 10, with 10 representing a perfect crystal. The following factors will be considered in judging quality: • match/mismatch with crystal type (out of 2) • presence/absence of occlusions (out of 2) • intact, clean and well-defined/broken, rounded edges (out of 2) • well-formed/misformed faces (out of 2) • clarity/muddiness (out of 2) Total Observed Quality Qo = x.xx (out of 10) The Total Score is then determined as follows: Total Score = [log (Mo+1)] x Qo The logarithm of the mass is chosen so that large poor quality crystals do not swamp out smaller good quality crystals. The value 1 is added to the mass so that crystals weighing less than 1 g get a positive score. A 100 per cent yield crystal made from 100 g (MMAX) that scores a perfect 10 on quality (QMAX) would get a theoretical maximum of: [log (100+1)] x 10 = 20.01 The actual score is expressed as a percentage of the maximum. The crystal with the highest Overall Score is the winning crystal. 100 x {[log (Mo+1)] x Qo} / {[log (MMAX+1)] x QMAX} = Overall Score % A perfect crystal weighing 100 g would get a score if 100%. Example: The best overall crystal in the 2001 contest with 150 g starting material (MMAX = 150 g) weighed 46.53 g and had a quality of 8.65. Its overall score was: 100 x {[log (46.53+1)] x 8.65} / {[log (150+1)] x 10} = 66.6%
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November 2019
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