Letter 24076

Heat-produced Patinas on Stainless Steel and Chrome [Washington] 

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We am creating a show car. Rather than using the usual chrome engine parts we have decided to attempt coloring the bolts with heat. The assumption is that, with hardened stainless steel bolts, this method of coloring would give a hardness that will stand up to being turned by a wrench, as well as a finish that will not change. We desire to have yellow and blue colors in both stainless steel and decorative chrome. So far I have heated some hardened stainless steel bolts to 550 degrees Fahrenheit. They turned a pale yellow. Then two days later they darkened to a nice yellow color.

My questions are:

Why did the bolts darken?
After heating the stainless steel or chrome plated bolts, is the surface just as hard?
Can I expect that at some point the color will stop changing and then remain the same (no oxidation)?
Is there a medium (the Incas (or Aztecs) used KNO3 (saltpeter) heated to its melting point to produce a beautiful tuqois patina on steel) I should use?
How hot do I need to heat chrome plate and stainless steel to get yellow and blue?
Is there a better way to have a hard surface with a metal yellow and a blue that won't oxidize or change color?

I would be grateful for any help.

Robert Myers
automobile repair/restoration - Tacoma, Washington, USA

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