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Temper Colors

Before the use of instruments such as pyrometers, colors were used to judge temperature when hardening and tempering. For example, on carbon tool steel where the tempering range may typically be from 200oC to 350oC, the color change with the rise in temperature giving light straw at around 210oC, Purple 275oC, and Grey at 330oC, The practice wtill continues in workshops where controlled heat treatment facilities are not available.