Ruby

Ruby is red corundum — aluminum oxide colored by chromium. By convention, the trade calls anything other than red corundum a “sapphire,” even if it’s pink. The line between “pink sapphire” and “ruby” is judgmental and the subject of decades of trade arguments.

After diamond, only ruby and sapphire are hard enough for true daily wear. A ruby engagement ring will outlive its setting.

Color

Color is the entire ballgame in ruby. Two stones at the same carat weight can vary 10× in price based on color alone.

The four color modifiers the trade cares about:

• Pure red — the ideal.
• Slightly bluish red — the “pigeon’s blood” range, most prized.
• Slightly purplish red — common, accepted.
• Orangish or brownish red — discounted.

Origin

Ruby is even more origin-sensitive than sapphire. Three regions dominate fine ruby pricing:

Treatments

Like sapphire, most ruby is heated to improve color and clarity. Heat is permanent, stable, and accepted by the trade. The danger zone is “lead glass filling” — a common treatment on cheap material where lead glass is melted into surface-reaching fractures. These stones are structurally compromised and will not survive ultrasonic cleaning or hot soldering. The trade doesn’t consider them “real” ruby for fine jewelry.

Always insist on a lab report disclosing treatments. “Heat only” is fine. “Glass filling” or “significant fissure filling” is a hard pass for an engagement ring or any piece you intend to keep.

Daily wear

At Mohs 9, ruby is the second-hardest gemstone after diamond. Wear it daily without ceremony. Clean it in warm soapy water with a soft brush. Skip ultrasonics if the stone is lead-glass-filled; otherwise they’re fine.