Red heat

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]
Colour	From	To	From	To
Black red^[2]	426	593	799	1,100
Very dark red	594	704	1,100	1,299
Dark red	705	814	1,300	1,497
Cherry red	815	870	1,498	1,598
Light cherry red	871	981	1,599	1,798
Orange	982	1,092	1,799	1,998
Yellow	1,093	1,258	1,999	2,296
Yellow white	1,259	1,314	2,297	2,397
White	1,315+		2,397+

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	977
Dull red	699	1,290
Dull cherry red	800	1,470
Full cherry red	900	1,650
Clear cherry red	1,000	1,830
Deep orange	1,100	2,010
Clear orange	1,200	2,190
White heat	1,300	2,370
White bright	1,400	2,550
White dazzling	1,500	2,730

References edit

^ Chapman, W. A. J. (1972). Workshop Technology, Part 1 (5th ed.). Burlington, MA: Elsevier Butterworth-Heinemann. ISBN 978-0713132694.
^ When viewed in dull light.
^ A Book of Steam for Engineers. Stirling Consolidated Boiler Company. 1905. p. 50. ASIN B006RXDG3W.

[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. p. 50. ASIN B006RXDG3W.

[1]

[2]

[3]

Red heat

Contents

Chapman edit

Stirling edit

See also edit

References edit