Cold Bluing hardware

[Tadpole]

I have seen the idea of heat treating tools and parts on the forum, but for small hardware I am trying cold bluing. I scuff each piece then dip them for about thirty seconds and they come out beautifully, but soon after they get coated in rust. Any chemist suggestions on how to combat this? Maybe gun oil?

[Scott_Conger]

what specifically are you bluing, and under what conditions are they being exposed to?

both of those make a big difference and will determine the best answer...

[RGould1910]

I had the same experience with the rust problem. I've accidentally"blued" a pice by heating. It was the steel end of a speedometer cable housing. It had a film of grease to begin with. The color was good, didn't rust and didn't wear off.

[Tadpole]

The pieces I have worked on are a zinc plated cotter pin, a raw nut, and a zinc plated oiler.
The photo makes the bluing look better than it is, they are gritty with rust. I am using Birchwood “super blue” which was advertised as being darker than their standard bluing.

[Scott_Conger]

true "bluing" is an oxide conversion coating on steel. As the steel is heated hotter and hotter, the oxide coating changes in thickness and reflects a number of colors, including purple, light blue, dark blue, brown, etc (not necessarily in that order) until it goes back to a silver color. Once the color you desire is attained through heating to a known temperature in an oven, or, the heat is removed (if a torch) and the part is dunked into oil, the color stops changing and an infinitesimal amount of oil is absorbed into the oxide layer. If you live in FL, the coating is very fragile and requires periodic coating with oil to remain rust-free. In WY where it is dryer, you can handle the part to your heart's content and it will be rust-free for almost forever so long as it is not subjected to moisture/perspiration and even at that, if wiped dry will remain rust-free.

Cold bluing on the other hand is an entirely different process and depending on the chemicals can be more or (far) less resistant to corrosion. With respect to blueing a zinc plated part, the color is not on the steel, but on the zinc. I have no experience with this, but suspect that using the chemical on the wrong material may be some of your undoing.

As an aside, blueing is not a heat-treatment per-se for steel when defining heat-treatment as altering the metallurgy of the basis part...you never want to heat-blue a tool that has to cut something as the heat required exceeds the tempering temperature by a significant degree...it will make the tool unuseable. That said, I heat blue much of my own tooling where aesthetics and mild rust-resistance are important (to me) and where hardness is NOT important to me.

when using cold bluing, or heat-bluing, surface condition and scrupulous cleanliness is paramount for the most pleasing and predictable appearance...a matte finish will give a dull/dark finish while a polished part will give a very lustrous finish when done

these two tools show the difference in amount of heat applied vs the color that resulted. They were made years ago and just taken out of storage to help another "T" guy with details of their manufacture...they still look like the day they were made

[Tadpole]

I thank you Mr.Conger, that was a very thorough explanation. I don’t think the cold bluing will work for me then, is paint my next best bet?

[Scott_Conger]

Personally I'd leave everything as bare zinc-plate. It will last a very long time so long as it is not subjected to road salt, and even then is pretty robust if rinsed thoroughly

if you're determined to use some other coating such as paint, you can dip the parts for a short time in Ospho and that will etch the zinc off pretty quickly and leave a matte finish on the bare steel which will readily accept primer/paint

a really excellent video of making, hardening, tempering and bluing a screw (including the color changes it goes through) can be found here: https://www.youtube.com/watch?v=Mx3qOMU9kGg

[Tadpole]

Thank you Mr.Conger, I will look into that.
My goal is to have all black hardware on this car.

[TRDxB2]

You might want to look into this Rustoleum product RUST REFORMER about $5 - not to be confused with their Rust Inhibitor
"Stop rust in its tracks with Rust-Oleum® Stops Rust® Rust Reformer. A layer of this flat-black coating bonds with rusty metal and instantly transforms it into a non-rusting surface. No need to sand down to bare metal, simply spray directly onto rust."

[pron022020]

Bluing with that product will not work over Zinc. I sandblast the parts I do and it produces a nice finish over. I usually put some oil on afterward. You will have to remove all of the zinc plating.

[Tmooreheadf]

I use muratic acid to remove the zinc coatings. Leaves a dark bare metal that can be treated however you desire.

[Henry K. Lee]

Very clean metal, warmed in the sun, multiple coats gives a nice appearance which is elements resistant. I only use this brand as it holds up.

To each their own!

Hank

[Scott_Conger]

Been thinking a lot more about this than I wanted to, but it has really stuck with me

now I know what has been bothering me: you want BLACK OXIDE, not bluing

once it hit me, I found this video which really shows it very well and is something I think you should consider: https://www.youtube.com/watch?v=TFfJwNvK1iY&t=1284s

whatever you do, good luck