From my limited experience of tempering some steel parts about 16" long
in a ceramic kiln at 290C, the colouration should be repeatable and even
if the part is clean and the temperature even. The parts I did were all
an even blue colour for a spring temper. IIRC the colour change for
stainless steel occurs at about 100C more than for steel, might apply to
chrome plate also.

T.Alan Kraus wrote:

Is there a chemical method for bluing chromed steel or aluminum? I
have seen color changes when chromed parts such as exhaust pipes are
heated, but in my mind heating does not create very predictable results.

cheers
T.Alan