GIA/GTL Master Stone Requirements (7.12)
GTL will not accept anything less than a .25 carat. A .33 carat would be better and a .40+ carat would be optimum. Even though a .25 carat is accepted it is more challenging to compare a much smaller diamond to a larger. You might ask “Why not go for a ½ or ¾ carat sizes for your masters”. This is fine, but the investment would be much greater, in contrast to the smaller counterparts.
Of course now with the lab-grown diamonds there are hybrid sets with the colorless masters being lab and the lower colors being natural. The subtle color differentiations in the yellow and brown hues are not practical in lab grown masters since they have a tendency to show slight grey influences.
Proportions are very important in the master stone requirements. Stones with the following negative characteristics would not necessarily be turned down but would be ill-advised.