I recently came across a Sotheby’s auction listing for a cushion-shaped sapphire ring weighing a whopping 17.29 carats, flanked by triangular diamond shoulders and mounted in platinum (size 53). The sapphire is Kashmir origin, which is extremely rare and highly prized for its unique, velvety deep blue hue often called “royal blue.”

This particular gemstone is untreated and supported by multiple authoritative gem reports: SSEF and Gübelin labs, dated 2024, plus an older SSEF report from 1996—all agreeing on its Kashmir origin and no heat treatment. The dimensions hover around 15.5 x 13.8 x 8.9 mm, with clarity showing minor natural inclusions and minor wear consistent with some age. The diamonds total roughly 1.0 to 1.2 carats (J-K color, VS-SI clarity). The auction estimated the lot at 500,000 to 800,000 CHF.

What impressed me is how provenance and treatment verification create real value beyond size alone. Untreated Kashmir sapphires are exceedingly rare, nearly legendary in collector circles. Its slight violetish blue tint and silky texture differentiate it from other sources. The auction’s condition notes explain some normal wear but affirm the piece remains in good condition.

For those collecting or investing in sapphires: how much more do you typically pay for confirmed Kashmir origin and no treatment? What other factors shift value big-time?

What Makes This 17.29-Carat Royal Blue Kashmir Sapphire So Valuable?