Ruby is the red variety of corundum, the exact same mineral as sapphire. The only difference is color: when corundum is red, it is a ruby; when it is any other color, it is a sapphire. Ruby gets its red from traces of chromium, which also causes a faint natural fluorescence that can make fine rubies seem to glow.
Color is everything
For ruby, color drives value more than any other factor. The most prized is a pure, vivid, slightly-blue red traditionally called "pigeon's blood." Too much purple, orange, or brown, or a tone that is too light or too dark, lowers the value. Because chromium both creates the red and tends to cause tiny fractures as the crystal grows, large clean rubies are genuinely rare, which is why top rubies can rival or exceed diamonds in price per carat.
Where the boundary with pink sapphire sits
Since ruby and sapphire are the same mineral, the line between a deep pink sapphire and a light ruby is subjective and has long been debated between trade centers. There is no single objective cutoff; it comes down to a judgment about where "pink" becomes "red."
Durability and the treatment question
Like sapphire, ruby is Mohs 9, extremely hard, with no cleavage, and excellent for daily wear. But the ruby market has one issue every buyer must understand:
- Heat treatment is common and accepted, improving color and clarity, and must be disclosed.
- Lead-glass fracture filling is extremely common in inexpensive commercial ruby. Heavily fractured, low-grade corundum is impregnated with lead glass to look like a solid gem. These "composite" or "glass-filled" rubies are far less durable: the glass can be damaged by heat, by common household acids such as lemon juice, and by ultrasonic cleaning. They should be described as a manufactured composite, not simply "treated ruby," and priced accordingly.
Ask one question
Before buying any ruby, ask directly whether it is heated only or glass-filled, and get the answer in writing. A modest natural, heat-only ruby is a very different (and more durable) product than a cheap composite that merely looks similar.
Natural vs synthetic
Synthetic ruby has been produced since 1902 and is common and cheap. It is real corundum but not natural, and must be disclosed as lab-created or synthetic. For any significant ruby, a report from a respected lab confirms both natural origin and the extent of treatment.
Caring for ruby
Natural and heat-only rubies are tough and tolerate normal cleaning, including ultrasonic. Glass-filled rubies are the exception and need gentle care: warm soapy water, a soft cloth, and no heat, acids, or ultrasonic machines.
Ruby is one of the great gems, but it is also one where the label matters most. Match the price to the product, insist on disclosure, and a natural ruby will reward you for a lifetime.
