Synthetic ruby
Synthetic ruby is genuine ruby grown in a few days in a factory, rather than over a few million years deep within the Earth's crust like its natural counterpart.
Either way, it's made from aluminium oxide, with a dash of chromium for colour (slightly more than you'd use to make sapphire). It's the same formula that nature uses to make it, only the factory's much faster, and making it on purpose.
The earliest and cheapest way to make ruby is the flame fusion method.
Synthetic ruby tends to be purer and so clearer than natural ruby. It's also much cheaper to obtain — as of 2025, you can get a 200g boule of synthetic ruby for under £20.
It's especially useful when making mechanical watches, and lasers and masers. When a watch's legend declares its jewel count, it's very likely talking about its number of synthetic rubies.
Mechanical watch materials: Ruby | Synthetic ruby
