How are rubies graded?

Rubies get graded mostly by how intense, pure and saturated the red looks; then the rest comes in later, like clarity, the cut quality and finally carat weight.

The top valued rubies show a vivid, deep red tone with a slight blue undertone; this has been called in the trade “pigeon’s blood” for a long while. Gemological labs check rubies to spot extra secondary colours such as orange or purple and those can lower the value. The grading documents also note any man-made improvements, for example, routine heat enhancement or lead glass filling, and those can hit the overall market price quite hard.