Look for reflections of blue and red within a ruby, as well as uniform color and small inclusions, or flaws, within the body of the stone. Bubbles, scratches and a stone that is too clear and perfect are indications that the stone may not be a genuine ruby.
Like sapphires, rubies are second in hardness only to diamonds. The deep red color is prized by many and leads to the stone's title of the king of all gemstones.
Step 1: Use a bright light
A bright light allows those examining rubies to see the clouds and inclusions in the stone, as well as reflections that can give clues to the stone's status as genuine or false. Most stones can be examined with the bare eye, but small stones may require using a jeweler's loupe.
Step 2: Look for uniform color
Even with inclusions and clouds, a ruby should have some uniformity of color throughout the stone. A genuine ruby should reflect red and blue light. Green and yellow reflections are an indication that the stone may not be genuine.
Step 3: Look for bubbles or inconsistent luster
Bubbles, inconsistent glow or scratches are key hallmarks that a stone may actually be made of glass. Since rubies are almost as hard as diamonds, few things can scratch them. Rubies may have clouds, but those clouds are still the same color and luster as the rest of the stone.
Step 4: Beware of perfect stones
Few rubies are truly perfect, and these stones tend to cost a pretty penny indeed. If a stone is touted as perfect and shows no flaws at all inside, the stone may not be genuine.
Step 5: Ask a certified gemologist
When in doubt, have a certified gemologist examine the stone. He can pinpoint whether the stone is genuine or not for certain.