Our 1.00ct and larger diamonds (and some smaller) have independent reports or certificates, mostly from GIA (Gemological Institute of America). Diamond grading is an art, not science. Two associates and I sent 16 diamonds to three major labs; not one received the same Colour and Clarity grade from all three labs.
‘Strictness’ order: GIA, IGI, HRD (Avoid EGL). Some small Australian labs are as strict as GIA. AGS is a small Las Vegas lab that tries to grade Cut effectively. GIA can only Cut grade round diamonds and their top ‘Excellent’ grade is universally known to be far looser than my patented system.
The Ideal-scope images mark GIA’s Excellent Cut Grade. Garry Holloway rejects GIA’s leaking “Excellent” Diamonds above the black line. Cutters produce more diamonds above that line because they get deeper heavier Carat weights.
At international conferences, I have asked directors of the world’s major diamond labs: “Would you buy a loved one a diamond based only on its cert?” None would. They know their own certs do not tell them how sparkly a diamond is.
These symbols are used on grading reports to indicate different types of inclusions and flaws. They are roughly in order from worst at the top to least of a worry near the bottom. The first listed at the top is the major grade maker: on the cert on below image the main grade maker is the Twinning Wisp.