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metal color change

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

Reply to
magboy7
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Certain that the Nickel alloy is the same ? A tiny gold delivers deep purple.

I'm not a metal expert, however I suspect the color is from the copper.

Are you cleaning before on all of them before heat ?

The color is from oxidation of the copper I rather expect.

You might not have an oxidation heat but a reduction heat if done by flame.

Those are my thoughts.

Martin

Mart> I need some advice.

Reply to
Martin H. Eastburn

Martin,

We are using a small oven. Heats to approx 400-450 maximum. Cleaning parts with kerosene before heating. When the oven was new, it was getting up to 500 dgrees and it seemes the color change was more consistent. Can the issues be the reduction in heat capacity? At what temp does copper start to turn blue?

Reply to
magboy7

The copper and if it has gold - it has to be in an oxidation state. The blue is copper oxide.

Sounds like the bad dude is the Kerosene and the oven not at 500.

The Kerosene is an oil base and that coats the metal preventing oxide. Likely the high temp burnt it off.

Try washing with something else. And then try it.

As to the temp - maybe you can blanket (high temp) the oven - or box it and increase the temp by lower loss.

Try with only a different wash.

I can't find an oxidation temp for metals. I'll continue to look.

Mart> >> Certain that the Nickel alloy is the same ? A tiny gold delivers deep purple. >>

Reply to
Martin H. Eastburn

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