Colour produced by heating titanium or zirconium — with a torch, oven, or flame — to grow an oxide film on the surface. The same interference principle as anodising, but the heat is less controlled than voltage, which is why flame-coloured pieces often show gradients: gold fading into bronze, bronze into blue, blue into purple.

The results are expressive and often hand-done, which means each piece is slightly different. A maker skilled with a torch can produce intentional gradients; a less controlled process produces accidental ones. Both have their followers.

Less durable than a properly anodised layer — the oxide from flame colouring is typically thinner and less even, and high-contact points can wear through to bare metal. Beautiful at purchase; check your expectations for longevity.