How can you identify a treated gemstone?

Gemmologists try to sort treated gemstones out by looking very closely for internal stress fractures, altered inclusion structures, dye concentrations that reach up towards the surface via cracks, or colour zoning that looks off when viewed at high magnification.

Different kinds of enhancements tend to leave specific forensic clues. Heat treatment in sapphires, for instance, often dissolves rutile silk, so you may see snowball-like or halo-like inclusions. Fracture filling in emeralds gets flagged by watching for the flash effect from the polymer resin, using specialised lighting, and not just casual observation. To be certain about modern diffusion or irradiation treatments, specialised lab gear is usually needed, like FTIR or Raman spectroscopy, because those tools can show signatures that plain visual checks miss.