Question

How can colors from heat tinting depend on temperature only?

Answer 1

Colors caused by heat tinting of a material can be listed by temperature.

For example, for carbon steel:

[...]

red:     260 °C  

purple:  270 °C  

violet:  280 °C  

[...]

from German: Anlauffarbe

That implies that the color caused by heat tinting of a given metal depends mainly on the temperature of the heat treatment used.

As I understand, the color depends on the thicknes of the oxide layer caused by the heating.

But I would expect that the oxide layer would grow over time at a given temperature, at least enough so that it's not negligible.

How comes the thickness of an oxide layer gets to a steady value in short time, and stays stable for a time on the order of minutes?

Answer 2

The colors appearing on metal due to heat tint can be an accurate indication of the surface texture.