Heat is a widely accepted treatment for ruby and sapphire. It can improve color or apparent clarity, and it is common enough that many buyers are advised to assume a ruby has been heated unless a laboratory reports otherwise.
What the laboratory can state. A respected laboratory records what its tests show at the time of examination. For fine-quality sapphire or ruby, confirmation of no evidence of heat speaks to rarity. The wording is careful. “No evidence of heat,” or, on a GRS report, “No indication of thermal treatment,” means the laboratory found no gemological signs—such as altered inclusions—that heat was applied. It is an expert opinion based on the evidence, not a guarantee that treatment could never have gone undetected, or that the stone cannot be altered later.
How to read the treatment line. On GRS reports for ruby and sapphire, “H” means enhanced by heat with no residues present. Further codes, from H(a) through H(d), describe residues of glass-like material in fissures or cavities; H(d) includes significant lead-glass filling, sometimes called a composite ruby. A color term such as pigeon’s blood or royal blue is not a treatment grade. On a GRS report it may be given to heated or unheated stones, so the treatment comment should be read on its own.
Ask for the report that belongs to the stone, and match it to the jewel in front of you. At Catharina Henrique Jewel Gallery, unheated colored gemstones are described as such, and a laboratory report—GRS, AIGS, or another lab—is noted when a piece includes one. Cœurs de Rubis, for example, is offered with an AIGS report for its unheated pigeon’s blood rubies. For a question of treatment or a 4K viewing, our Private Concierge is available on WhatsApp.