How do professionals grade gemstones?

Professionals typically grade coloured gemstones by giving subjective yet standardised values to what they see in hue, tone, and saturation, while at the same time measuring clarity, carat weight, and the crispness of how the facets are laid out in a way that is consistent.

Unlike diamonds, which follow a single universal grading framework, coloured gem grading leans a lot on the evaluator’s own know-how and the quality of the reference colour sets. In practice, gemmologists hunt for the cleanliness of the dominant colour, aiming for vivid saturation without the stone looking overly dim or swallowed by shadow. Clarity is judged with regard to the gem’s category, because certain stones (for example, emeralds) are commonly expected to show inclusions, whereas other varieties are supposed to be eye-clean.