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Type of coating/plating on mild steel - What is your best guess based on color?

Looks like that could be the natural oxide layer from tempering, or from precipitation hardening. Both would preclude it being mild steel; are you sure of the material?
 
totally depends on how old it is, and what it came from.
Could be copper plated, could be an oil paint, could be auto body lacquer, could be powdercoated- all were used at different times for different products.
 
I'd guess it's a faded or light cold blackening:

Do-It-Yourself Cold Blackening :


Modern Machine Shop


It looks far too thin to be a powdercoat, or even a plating. But heck, trying to identify it from a picture without a good color reference is asking a lot.

Yes, I may be asking much. It is not critical to identify it. I was just wondering if anyone recognized it right-off-the-bat.

I make many parts for this customer. This was done by another shop (no longer in business) years ago. The customer does not know the plating. Many of his unhardened parts are either painted, black oxide, or left raw. This is none of the above.

If we know the coating/plating then we continue with it, if not we generally don't bother.

This is not worth a long discussion. If it looks familiar to anyone, respond. Otherwise, no big deal.

Thanks,

Bill
 
If you take a very clean and oil free steel part and dunk it in copper sulfate solution it will acquire a very thin coating of copper. Used to be done for anti seize properties. It will be bright and this looks tarnished. You might give it a try and see if that is it.
 








 
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