18k white gold Sapphire Ring

The most critical factors are colour saturation, hue, and tone — with highly prized specimens showing a vivid, medium-dark blue free of grey or brown modifiers. Origin also plays a significant role, as sapphires from Kashmir, Burma, and Ceylon historically command premiums for their distinctive optical character. Clarity, cut precision, and whether the stone is unheated or minimally treated round out a collector’s assessment.

Heat treatment is a widely accepted practice in the trade, used to improve colour and clarity by dissolving silk inclusions at high temperatures. Unheated sapphires — those with no evidence of thermal enhancement — are considerably rarer and typically command a substantial premium, particularly in fine sizes above two carats. Reputable gemological laboratories such as GIA, Gübelin, and SSEF can certify heat-treatment status, which is essential documentation for serious collectors.

Some sapphires exhibit asterism — a six-rayed star effect caused by intersecting needle-like rutile inclusions oriented along the crystal’s optical axis, best seen under a direct light source. Colour-change sapphires represent another notable phenomenon, shifting between blue in daylight and violet or purplish tones under incandescent light. These optical effects are entirely natural and significantly influence a stone’s rarity and desirability.

Sapphire ranks 9 on the Mohs scale, making it highly resistant to scratching in everyday wear — second only to diamond among commonly set gemstones. Cleaning with warm water, mild soap, and a soft brush is safe and effective; ultrasonic cleaners are generally suitable unless the stone has significant fractures or fracture-filling treatments. It is advisable to have the setting checked by a qualified jeweller annually to ensure the metal prongs retain their integrity and the stone remains secure.