Blueing solutions

You know those stuff for blueing guns back in the states… except I’m not blueing guns but some machined parts out of steel. I want to blue them so they don’t rust and make them look good…

When I was in the school metalworking class we “blued” metal items by heating them up and then plunging in to an oil bath

Wouldn’t that affect the heat treat of the item? I mean if you heat something for the steel to turn blue in the air it’s ruined as far as heat treatment goes…

But I know rust bluing… did it on gun parts back in the states. They work but takes forever to do.

It would be nice if someone can bring some Blue Wonder, but I don’t know if this will get flagged by customs.

I suppose it would depend on the temperature, the lesson was a long time ago but I do remember it was simply judged by appearance, there was a rough guideline about the surface appearance and corresponding temperature. The item is still in my toolbox today and hardly shows any rust. 45 years later!

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OK, I found here some links to guidelines, so it seems you could go up to about 210’C which is faint yellow and remain below the tempering temperature for knives.

…of course you could nowadays use a cheap IR thermometer to check surface temperature during the process, but judging it by eye seems far more craftsmanlike don’t you think?

It’s still in my toolbox here!

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Rust blueing is much safer. But if your steel is mild steel then it doesn’t matter, as you can heat it til it’s red hot and it wouldn’t change anything.

Have you considered lurking on some gun forums, maybe you could discover a recipe for making your own blueing solution.
I know there are industrial treatments called “black oxide” or “phosphating” (iron phosphate or ferrous phosphate) - they create dark corrosion-protecting surfaces in a process using phosphoric acid I believe.

I’m scared to hang out at gun forums. Guns aren’t legal in Taiwan and penalty for making them is quite severe (death penalty is possible in fact, not that it’s ever used unless you were supplying guns to gangsters who used it to murder someone important). So last thing I want is some cop following me on some gun forum and I end up getting a visit when I least expect it.

No one did this yet?


OK, here we go, not a gun in sight, only gear wheels and industrial stuff. I also recall that Manganese Phosphate is somewhat superior. Quite a messy proess to do DIY though…

It just seems like it may be easier for me to send parts to a third party for coating. I know of a shop that does anodizing for you, but not sure about coating for steel. If the part is small you could probably do rust bluing DIY but for bigger parts, like say a piece of steel the size of a table, 1" thick, better to send those in. I’d need a crane to lift it for one thing.