Very Important Diamond ring

The cut-cornered rectangular step-cut diamond weighing 18.37 carats, on a band set with brilliant-cut stones, mounted in platinum, size 53.

Stamped PT950 for platinum. Accompanied by GIA report no. 17426020 stating that the diamond is D Colour, Flawless, with excellent Polish and Symmetry. Further accompanied by a GIA type classification report stating that the stone is a Type IIa diamond. Hardly any signs of wear, condition as new.
"In response to your inquiry, we are pleased to provide you with a general report of the condition of the property described above. Please note that colour, clarity and weight of gemstones are statements of opinion only and not statements of fact by Sotheby's. We do not guarantee, and are not responsible for any certificate from a gemological laboratory that may accompany the property. We do not guarantee that watches are in working order. Prospective buyers should inspect each lot to satisfy themselves as to condition and must understand that any statement made by Sotheby's is merely a subjective, qualified opinion. Prospective buyers should also refer to refer to any Important Notices regarding this sale, which are printed in the Sale Catalogue, in particular to the Notice regarding the treatment and condition of gemstones and to the Notice regarding import of Burmese jadeite and rubies into the US.
NOTWITHSTANDING THIS REPORT OR ANY DISCUSSIONS CONCERNING A LOT, ALL LOTS ARE OFFERED AND SOLD "AS IS" IN ACCORDANCE WITH THE CONDITIONS OF BUSINESS PRINTED IN THE SALE CATALOGUE."

Scientists classify diamonds into two main 'types' - type I and type II - based on the presence or absence of nitrogen which can replace carbon atoms in a diamond's atomic structure. These two diamond types can be distinguished on the basis of differences in their chemical and physical properties. Type II diamonds contain little if any nitrogen and they are subdivided into two groups (IIa and IIb) both of which are quite rare (less than 2 % of all gem diamonds).
According to the records of GIA Laboratory, the 18.37 carat cut-cornered rectangular step-cut diamond described in the GIA Colored Diamond Grading Report # 17426020 has been determined to be a type IIa diamond. Type IIa diamonds are the most chemically pure type of diamond and often have exceptional optical transparency. Type IIa diamonds were first identified as originating from India (particularly from the Golconda region) but have since been discovered in all major diamond producing regions of the world.
Among famous gem diamonds, the 530.20 Cullinan and the 105.60 Koh-i-noor are examples of type IIa.'