ForMatter/Finishes/patina/Heat-tinted blue (steel)
finish_patina_heat_blue

Heat-tinted blue (steel)

patina · colored · heat blue, tempering color blue, peacock blue

Heat steel in air to 300 °C and the surface grows a thin oxide that reads peacock blue. A traditional gunsmith finish, the blued screws on a watch movement, knife maker's bolster decoration. The color is the oxide — clean it off, you remove the color.

Thin-film interference colors from controlled oxidation of carbon / tool steel in air. Color sequence by approximate temperature: pale straw 220 °C, dark straw 250 °C, brown-purple 270 °C, peacock blue 290 °C, dark blue 310 °C, gray 330 °C+. Layer is ~50–200 nm of magnetite (Fe₃O₄). Doubles as low-temperature temper indicator on tool steel. Soft, easily polished off; coat with thin oil or wax to preserve.

character — deep blue with a faint metallic sheen, fragile, traditionally hand-applied, wears naturally.

Finish properties

  • levelcolored
  • subcategorythermal oxide
  • applies tometal
Produced by processesHeat Treatment of Steel

Second life

reversibilitymoderate — patinas can be stripped (acid, mechanical polishing) and re-applied; the substrate metal is preserved through the process. The historical patina cannot be exactly reproduced after stripping.
blocks substrate recyclingno
renewabilityfield-renewable — a patina can be refreshed or applied to a stripped piece by a metalsmith with the right chemistry. Conservation-grade re-patination is a specialty (Sculpture Conservation Studio practice).

Hughes & Rowe *The Colouring, Bronzing and Patination of Metals* (Crafts Council, 1991, Watson-Guptill ed. 1995); American Institute for Conservation patina-conservation guidelines.

Citations