1. A method for generating a look-up table for use in clarity grading a gem comprising: collecting actual inclusion parameter data and an associated clarity grade for each of a plurality of gems; deriving from the actual inclusion parameter data and the associated clarity grades statistically sound mathematical relationships which model interactions between clarity grades and combinations of inclusion parameters; and associating parameterized clarity grades with corresponding combinations of inclusion parameter value ranges based upon the derived mathematical relationships, so that for a set of input inclusion parameter values a corresponding parameterized clarity grade is provided; wherein the collecting step includes collecting the inclusion parameter data as parameterized inclusion characteristics, including a parameterized position, a parameterized relief, and a parameterized number of inclusions or reflections; and wherein the parameterized position includes Table, Table-Crown, Crown, and Girdle values; wherein the parameterized relief includes three possible values; and wherein the parameterized number of inclusions or reflections includes Clarity Grade degrading adjustment values determined as a function of ranges of numbers of inclusions or reflections.