Ruby is red chromium-colored corundum. Hue, tone, saturation, fluorescence, transparency, inclusions, and cut interact; darkness alone does not make a ruby fine.
What to notice in ruby
Begin with the material rather than a romantic name. Look at color in more than one light, then study transparency, inclusions, polish, symmetry, and face-up brightness. In a faceted stone, check for a pale window through the center and dark extinction that stays fixed as the stone moves. In a cabochon or carving, judge the surface, outline, pattern, and any optical effect from several angles.
Carat weight is not a measurement of visible size. Compare the millimeter dimensions and depth as well. A deep stone can carry hidden weight; a shallow one may spread well but lose color or brilliance. Photographs should show the individual piece, and a slow video can reveal movement that a still frame misses.
Wear, care, and disclosure
Ruby has a Mohs hardness of approximately 9, but hardness only describes resistance to scratching. Cleavage, brittleness, inclusions, thin edges, and setting style also affect how safely a gem can be worn. Heating is common, while fracture filling and diffusion require especially clear disclosure; origin should be presented as a laboratory opinion when it materially affects value.
Ask what is known about identity and treatment, what has been independently tested, and which details remain undocumented. Geographic origin should not be guaranteed from appearance alone. A laboratory report can be sensible when identity, treatment, origin, or price would materially change the decision.
Browse the current collections to compare available examples. For a wider inspection method, read the natural gemstone buying guide and the treatment disclosure guide.