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.

Chapman[edit]

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

Colour Temperature [°C] Temperature [°F]
From To From To
Black red[2] 426 593 709 1010
Very dark red 593 704 1010 1210
Dark red 704 814 1210 1408
Cherry red 815 870 1409 1508
Light cherry red 871 981 1510 1708
Orange 981 1092 1708 1908
Yellow 1093 1258 1910 2207
Yellow white 1259 1314 2209 2308
White 1315+ 2309+

Stirling[edit]

In 1905 Stirling Consolidated Boiler Company published a slightly different set of values[3]

Colour Temperature [°C] Temperature [°F]
Red: Just visible 525 980
Dull red 700 1300
Dull cherry red 800 1500
Full cherry red 900 1700
Clear cherry red 1000 1800
Deep orange 1100 2000
Clear orange 1200 2200
Whitish 1300 2400
Bright white 1400 2600
Dazzling white 1500 2700

See also[edit]

References[edit]

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