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Heat-produced Patinas on Stainless Steel and Chrome
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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 turquoise 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 M [last name deleted for privacy by Editor]automobile repair/restoration - Tacoma, Washington
December 27, 2008
Wow.
Why did the bolts darken?
Most likely an oxidation reaction.
After heating the stainless steel or chrome plated bolts, is the surface just as hard?
probably not, although the underlying bolt strength shouldn't be greatly affected by that temperature.
Can I expect that at some point the color will stop changing and then remain the same (no oxidation)?
It will depend upon the grade of stainless (amount of nickel & chromium in the alloy.)
Is there a medium (the Incas (or Aztecs) used KNO3 (saltpeter) heated to its melting point to produce a beautiful turquoise patina on steel) I should use?
Since neither the Inca nor the Aztecs used iron, much less steel, I'm not sure about this information....
How hot do I need to heat chrome plate and stainless steel to get yellow and blue?
Sorry, don't know.
Is there a better way to have a hard surface with a metal yellow and a blue that won't oxidize or change color?
There is a technique for anodizing stainless--used to be a company in Colorado that used it for making signs, I do not know what the process is--but it must be out there, google is your friend.
Depending upon how "hard" the surface needs to be, you could also use titanium bolts, which can be surface colored to a dozen shades, everything except red.
This process is highly controllable since it can be done using controlled voltages--each voltage will represent a color. You can color different parts of pieces this way--even put pictures on the surfaces.
But while the surface will stand up to handling, it's likely that any burr or scratch on a wrench would scratch through the oxide. That said, it could be done in situ.
These colors are stable unless voltage or heat is applied to the surface. The oxide must be physically removed in order to start the process.
- Menomonie, Wisconsin