I need some advice.

I am taking stamped metal parts (nickel silver) and heating them up to
about 450 - 500 degrees. Many of them change color from a shiney
silver to a bluish color. This is the effect I want.

Lately, many of the parts are not changing color. When stamped, we
use a light coating of kerosene for die lube. Sometimes we run fairly
dry.

IS the color change a result of the light kerosene? Is it a function
of temperature? What can I do to ensure that all the parts turn
bluish?

Thank You,


Wayne