The cushion-shaped diamond weighing 5.20 carats, size 6.

Accompanied by GIA report no. 17424000 stating that the diamond is D color, Internally Flawless. Together with a letter from the GIA stating that the diamond has been determined to be type IIa. Very unusual and elegant shape with nice brilliance. Very well mounted. In very good condition.
In response to your inquiry, we are pleased to provide you with a general report of the condition of the property described above. Since we are not professional conservators or restorers, we urge you to consult with a restorer or conservator of your choice who will be better able to provide a detailed, professional report. 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. Illustrations in the catalogue may not be actual size. Prospective purchasers are reminded that, unless the catalogue description specifically states that a stone is natural, we have assumed that some form of treatment may have been used and that such treatment may not be permanent. Our presale estimates reflect this assumption.
NOTWITHSTANDING THIS REPORT OR ANY DISCUSSIONS CONCERNING CONDITION OF A LOT, ALL LOTS ARE OFFERED AND SOLD "AS IS" IN ACCORDANCE WITH THE CONDITIONS OF SALE PRINTED IN THE CATALOGUE.

Accompanied by GIA report no. 17424000 stating that the diamond is D color, Internally Flawless.  Together with a letter from the GIA stating that the diamond has been determined to be type IIa. 

Also accompanied by Gübelin report no. 1011150 stating that the diamond is D color, Internally Flawless, and a note from Gübelin stating that diamond is classified as a type IIa.  Together with an appendix from Gübelin stating that the diamond possesses an antique cutting style which is rarely encountered in the gem trade today, and diamonds of this type, exhibiting an antique cutting style as well as a superior quality, are very rare and will most certainly evoke references to the historic term of 'Golconda'.

For centuries, India was the sole source of diamonds to the world.  And of the many diamond mines in India, the Golconda mines were the most famous, producing some of the world's best-known diamonds including The Koh-i-Noor and The Hope.  A Golconda diamond is distinguished by a high degree of transparency as a result of the purity of its crystal, resulting in a limpid quality that is reminiscent of a drop of ice water.  It also represents a specific type of pure carbon known as type IIa, containing no significant amount of nitrogen in its crystal lattice.  The absence of nitrogen, the element which imparts a yellowish hue to diamonds, results in a diamond that is colorless and often said to be beyond white.  With less than 1% of the world's diamonds classified as type IIa, this pure diamond is as rare as it is beautiful.