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WARNING: Yet More Metal Working Content - Tool Blackening

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  • WARNING: Yet More Metal Working Content - Tool Blackening

    Cold bluing or cold blackening seems to be an accepted method of protecting steel parts in the shop. Add on a sealant or keep the part oiled and supposedly it will resist rust and corrosion indefinitely.

    I have done cold bluing in the ancient past using the gunsmith supplies. When I was a kid I stripped and refinished an old Sears .22 rifle, and I built 4 different black powder kit guns that came in the white.

    The quantity in gunsmith supplies is rather stingy. The amount in a bottle is enough to do a fair to good job on one complete firearm and maybe do some touch up work if you know how to make it blend. Two guns if you don't make any mistakes.

    More recently I've started making tools in my own shop. Many were intended to be a single use or short run tool. Long reach clamp to hold a slide bar in a mold until it could be match machined and clamped in other ways. Long reach tool holder for deep milling. Half round tool for work stop in the spindle and work positioning. Lots of stuff really. Mostly I have left them in the white (fine for carbide tools and some I've made in stainless) because they were made to do a single job. I didn't throw them away, but I didn't plan for them to be likely to see future use. It turns out nearly all of them have been much more useful than I originally planned. I need to blacken and oil them I think.

    Not wanting to go with a stingy little bottle from a gunsmith supply I looked at McMaster and MSC. They both stock some form of steel tool black. It seems expensive, but its a larger quantity than your local retail bottle of gun blue. How long does it really last? Is the "sealant" in some of those kits better than just oiling the part? Is it just oil? I don't mind spending the money. I just want to know its worth it.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    If the small bottles of cold blue are the issue, Brownell's sells their excellent OXPHO-BLUE in quarts (32-oz) as well as a stingy 4-oz half-cup.
    SE MI, USA


    • #3
      If you're keen on this you might also look into a home Parkerizing setup. The finish it produces is not as thin but it holds oil far more tenaciously than cold blued surfaces. And it's a fair amount more durable against scuffing than a cold blue. And from a couple of YT videos I watched on it a couple of years ago requires relatively minimal gear and the chemical isn't wildly dangerous.

      Being as it has SOME buildup compared to cold blue you might want to mask off some critical surfaces. But then there may be a way to control any buildup it causes too?

      Chilliwack BC, Canada


      • #4
        Quinn Dunki (Blondihacks) uses either Oxpho-blue or Jax. I don't know how she compares them.

        I tried this rust conversion process. Results similar to cold blue, mabe a little closer to black. Simple, safe but a lot more work. I won't repeat.


        • #5
          I use ammonium nitrate, at a rolling boil on the stove. Works really well and sucks up pull like a sponge. Markx did a nice write up on here which I followed


          • #6
            Not having access to ammonium nitrate in reasonable qty (not a farmer), I did the old rust blueing, and it turned out pretty well on the first thing I tried it on, which was a turret lathe tool.

            I just made up some salt water, dunked the part and let it rust in air. a couple dunks per "round". Knocked off the flaky stuff with a brush, and boiled it. after third round or so of that, parts were a nice black.

            Results good, and the materials are plentiful.

            The thread is on here, last year I think, complete with process used and results pics (as well as relevant replies, irrelevant replies and a few plain snarky replies, for your amusement).
            CNC machines only go through the motions


            • #7
              I got my AN from a friend at work


              • #8
                For pieces that can stand heating without losing precision of function, I often do this.

                Heat the part until it starts to run color. straw, to blue . Then the piece is plunged into clear mineral oil . If a black finish is wanted, used motor oil blackens right up.

                Lots of smoke, and some fire, so best done outdoors. But I have some pieces over 40 years old and they still "look good" . Wipe down with an oily rag from time to time.