Cornflower blue

"Cornflower blue" is the trade name for the velvety medium-blue tone historically associated with Kashmir sapphire. The color reference is the cornflower (Centaurea cyanus), a soft medium blue with slight violet undertone and a characteristic muted, "velvety" character that distinguishes it from the more saturated and brighter blues of other sapphire sources. SSEF and Gübelin sometimes use "cornflower blue" as a color description on the supplementary remarks of origin reports for Kashmir sapphire and for stones from other sources whose color matches the Kashmir reference.

The velvety character comes from microscopic rutile inclusions (silk) that scatter light inside the stone. The silk softens the apparent saturation and produces the velvety, slightly hazy character that defines the Kashmir aesthetic. Other sapphire sources — Mogok, Ceylon, Madagascar — produce blues without the silk-driven velvet, which is why even color-matched stones from those sources do not look identical to Kashmir under careful examination.

Heat treatment destroys silk. The high temperatures used in traditional sapphire heat treatment (1,400 to 1,800 degrees Celsius) dissolve the rutile needles into the corundum lattice, improving transparency and color saturation at the cost of the velvety character. Heated cornflower-blue sapphires look brighter and more saturated than unheated Kashmir but lose the signature velvet — which is why investment-grade Kashmir sapphires are almost universally unheated and command multiples of heated equivalents.

The "cornflower blue" term is used loosely outside the trade. Online listings and retail marketing apply the term to almost any medium-blue sapphire, particularly those with a slight violet modifier. The trade-recognised meaning requires the velvety character and the medium-blue tone in combination; a saturated bright medium blue without the velvet is not cornflower blue in the trade sense, even if the basic hue matches.

For Kashmir sapphire specifically, "cornflower blue" is the visual signature that anchors the country-of-origin call. SSEF and Gübelin make the Kashmir origin determination via trace-element chemistry (LA-ICP-MS) plus inclusion-fingerprint comparison; the cornflower-blue color is the visible signal that flags the stone for the chemistry. Stones that match the chemistry but not the color (or vice versa) are called as Kashmir only if both align.

The term is one of three named color calls in sapphire trade vocabulary, alongside "royal blue" (a deeper, more vivid blue associated with Mogok) and "padparadscha" (the pinkish-orange call). Each carries pricing weight at the top of the market when issued by SSEF or Gübelin.