July Birthstone: Ruby

• Fine rubies are a pure, vibrant red to slightly purplish red. The red comes from chromium.
• Ruby is the most valuable variety of corundum, the mineral that also makes sapphire.

• Rubies are often heated to remove a purplish tint and leave a purer red; heat can also clear the fine needle-like inclusions called silk. Heat treatment is stable and accepted in the trade.
• Less common treatments are lattice diffusion and dyeing. Lower-quality stones may have cracks and cavities filled with glass so they look clearer, and some of these treatments make a ruby easier to damage in normal wear.
• Before you buy, ask whether the ruby is treated and by what method. In the US the Federal Trade Commission requires sellers to disclose treatments that affect value, and a GIA identification report shows whether a stone is natural or synthetic and how it was treated.
• Ruby was the first gem made in a laboratory: Auguste Verneuil announced his flame-fusion process in 1902, and flame fusion is still the cheapest and most common way to make lab-grown ruby.

Ruby is 9 on the Mohs scale, second only to diamond, with excellent toughness and no cleavage (a tendency to split when struck). GIA says that makes it a great choice for rings worn every day, as long as no treatment has weakened the stone.

• In ancient India ruby was called the "king of precious stones".
• Burmese warriors believed ruby made them invincible in battle.

• Warm, soapy water and a soft brush: always safe.
• Ultrasonic cleaner: usually safe for untreated and heat-treated stones.
• Steam cleaner: usually safe for untreated and heat-treated stones.

Glass-filled or dyed rubies should only be wiped with a damp cloth.