Red heat

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For other uses, see Red Heat (disambiguation).

The practice of using colours to determine the temperature of a piece of (usually) ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it and the only way to do this was to heat it up to a colour which was known to be best for the work.


According to Chapman's "Workshop Technology" the colours which can be observed in steel are:[1]

Colour Temperature [°C]
Black red (when viewed in dull light) 426 to 593
Very dark red 593 to 704
Dark red 704 to 814
Cherry red 815 to 870
Light cherry red 871 to 981
Orange 981 to 1092
Yellow 1093 to 1258
Yellow white 1259 to 1314
White 1315+


In 1905 Stirling Consolidated Boiler Company published a slightly different set of values[2]

Colour Temperature
Red: Just visible 525 °C (980 °F)
Dull red 700 °C (1,300 °F)
Dull cherry red 800 °C (1,500 °F)
Full cherry red 900 °C (1,700 °F)
Clear cherry red 1,000 °C (1,800 °F)
Deep orange 1,100 °C (2,000 °F)
Clear orange 1,200 °C (2,200 °F)
Whitish 1,300 °C (2,400 °F)
Bright white 1,400 °C (2,600 °F)
Dazzling white 1,500 °C (2,700 °F)

See also[edit]


  1. ^ Chapman, W. A. J. (1972). Workshop Technology, Part 1 (5th ed.). Burlington, MA: Elsevier Butterworth-Heinemann. ISBN 978-0713132694. 
  2. ^ A Book of Steam for Engineers. Stirling Consolidated Boiler Company. 1905. ASIN B006RXDG3W.