Choosing Master Stones (7.11)
We can select our own diamonds to send to GIA for a master stone report. It’s important to understand that specific requirements have to be met before GIA will accept a stone as a master.
Choosing master stones is a task in itself. Unless you have a lot of contacts in diamond suppliers, finding the prerequisites required for a master stone will be difficult to say the least. There will definitely be a hefty premium on a single or a set of master stones, so be prepared for sticker shock.
Thick to Extremely Thick Girdles
Crown heights less than 11%
Pavilion depths less than 40% or greater than 45%
Old style cuts
*Damaged stones or dirty girdles
Medium to strong fluorescence (discussed in 7.41).
SI2 to Imperfect clarities visible through the
pavilion with your naked eye
Thin to slightly thick girdles (faceted is ok)
Crown height 12% to 15%
Pavilion depth 42% to 44%
Modern round brilliants
A stone without damage and clean girdle
None to faint fluorescence
SI1 or better, without dark inclusions
Faceted girdles are preferred since gray girdles will collect embedded debris in pits caused in the cutting process leaving behind an unwanted color influence.