Natural or synthetic ruby: how to tell them apart

Synthetic rubies have been grown since the 19th century — same corundum, but far cheaper. The problem is selling synthetic as natural.

Red flags A too-clean stone at a low price; perfectly even colour; a seller who avoids talk of a report.

Under the microscope Natural inclusions (crystals, rutile "silk") vs synthetic gas bubbles and curved growth lines. Only a gemologist's report is reliable.