Heat coloring of metals

Heat coloring of metals is a relatively simple process that, in principle, produces interference colors on the surface of the metal .

The colors depend on the temperature to which the metal is heated.

Heat coloring of metals can also include procedures for obtaining brown or black color by gradually heating objects made of gilt copper (also known as vernis brun) or steel coated with linseed oil to 300 - 400 C.[1][2][3] This process also includes the Bower-Barff process, and related processes, in which the steel is heated to 800 C and exposed to highly heated steam.

[6] straw yellow/232 C brown/265 C purple red/277 C light blue/288 C dark blue/293 C[7] light yellow/290 C brown/390 C magenta/450 C blue/540 C dark blue/600 C[8] pale gold straw/385 C purple/412 C deep blue /440 C red purple/565 C light green/510 C brown gray/648 C green blue/925 C[9] Heating to a temperature of 161-341 C produces various interference colors[10] Hiorns, A.

The Chemical Coloring of Metals and Allied Processes.

Scale of colors obtained by heat coloring of steel.This process is known as tempering when it is applied to the hardening of tools made of steel.
The various colors produced indicate the temperature the steel was heated to. Light straw indicates 204 °C (399 °F) and light blue indicates 337 °C (639 °F)
Blackened steel test plate,oiled with linseed oil and then heated to 300 - 400 C
Titanium test plate,colored by heat
Stainless steel plates,coloured by heat tinting