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Anyone done hot caustic bluing?

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  • #31
    I know the purity the same way you do, read what it said on the container "contains potassium nitrate". I know the other ingredients that same way, " " it said nothing about them. Sure , we have hard water. OK, and?

    It's been in there for 25 minutes again, after an overnight soak in purple, and an acid dip. The gray spot was removed, but now is back, and is approaching black, in the same location as before. The rest of it is nearly as shiny as stainless. And, no, it is NOT stainless. I'd know if it was..... After machining the entire thing, I believe I would "probably have noticed"...........

    That "use potassium nitrate" thing is beginning to sound like "fake news". The only thing saving it is that a scraggly spot is indeed turning color.
    1601 2137 5683 1002 1437

    Keep eye on ball.
    Hashim Khan

    If you look closely at a digital signal, you find out it is really analog......

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    • #32
      I was talking about hot caustic bluing, there you can swap the AN for easier to find potassium nitrate. I don't use the other process that was linked because it requires AN and I can't find it, so I fume blue or use hot caustic bluing. Or I phosphate (parkerize).

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      • #33
        So the "markx method" will ONLY work with AN? 'Cause it's putting a killer black spot on this tool. Just not touching the rest, and I've cleaned and acid dipped it.
        1601 2137 5683 1002 1437

        Keep eye on ball.
        Hashim Khan

        If you look closely at a digital signal, you find out it is really analog......

        Comment


        • #34
          I honestly wouldn't know, I've never tried it, you're in unknown territory now

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          • #35
            Originally posted by tlfamm View Post
            Nobody has knocked yet ...
            You haven't ordered enough yet

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            • #36
              Originally posted by tlfamm View Post
              @JoeLee: "I wouldn't advise using distilled water"

              ???
              Because distilled water could be contaminated from aluminum or copper condenser coils compounded by the large volume of air flow over the coils introducing other contaminates into it.. Traces of these elements can cause problems with the process / results.

              Water with too much iron, can also cause issues. But there have been few reported issues with tap and well water.

              JL.................



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              • #37
                Originally posted by J Tiers View Post
                I know the purity the same way you do, read what it said on the container "contains potassium nitrate". I know the other ingredients that same way, " " it said nothing about them. Sure , we have hard water. OK, and?

                It's been in there for 25 minutes again, after an overnight soak in purple, and an acid dip. The gray spot was removed, but now is back, and is approaching black, in the same location as before. The rest of it is nearly as shiny as stainless. And, no, it is NOT stainless. I'd know if it was..... After machining the entire thing, I believe I would "probably have noticed"...........

                That "use potassium nitrate" thing is beginning to sound like "fake news". The only thing saving it is that a scraggly spot is indeed turning color.
                The mystery spot could be a hard spot in the material, or a spot that was welded at one time.... different material in that area?? don't know what your part is...any pics?? Just guessing here. I've ad a few surprises but I've always found the problem.

                25 minutes in the hot salts seems a bit long. Usually the recommended time is about 15 min. Temp issue?? what is your boiling point??

                It's typical for the solution to turn brown after a few uses and teh foam and scum is also typical, sometimes it goes away with the rolling boil.

                How stable is your temp?? small shallow tanks with large surface areas difficult to keep stable because of the evaporation rate. You have a little leeway with the temp variations, like + - 5 deg, of 285 degrees.


                JL..................



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                • #38
                  So, what I get after 40 minutes is this. A little rusty, one black spot that may have been there already, now that I consider the matter, and that's the lot. I think this one is going to have to go up to 800F and get dunked in oil. I know that works, but did not want to do it with this.

                  Dirty oil quench also works, but this part would be better blued much colder.

                  I will guarantee you that this is not at 285.... boiling point is much lower. Maybe with a pressure pot.

                  It was "regular clean steel color" originally. Air is getting to it, because it has rusted. it boiled for 40 min to get here. It's clean and has been acid dipped, it's in the acid again.

                  The dark spot is probably in the steel, cause unknown, turned from 2" rod stock.



                  Last edited by J Tiers; 09-25-2020, 03:32 PM.
                  1601 2137 5683 1002 1437

                  Keep eye on ball.
                  Hashim Khan

                  If you look closely at a digital signal, you find out it is really analog......

                  Comment


                  • #39
                    Originally posted by J Tiers View Post
                    So, what I get after 40 minutes is this. A little rusty, one black spot that may have been there already, now that I consider the matter, and that's the lot. I think this one is going to have to go up to 800F and get dunked in oil. I know that works, but did not want to do it with this.

                    Dirty oil quench also works, but this part would be better blued much colder.

                    I will guarantee you that this is not at 285.... boiling point is much lower. Maybe with a pressure pot.

                    It was "regular clean steel color" originally. Air is getting to it, because it has rusted. it boiled for 40 min to get here. It's clean and has been acid dipped, it's in the acid again.

                    The dark spot is probably in the steel, cause unknown, turned from 2" rod stock.



                    That spot looks like it may be pitting or corrosion in the steel. 40 minutes in the bath is way too long..... something is wrong all you need is 15 min. max in the proper solution and temp to get the steel as black is it's ever going to get. There is no way your going to get proper blackening below 285. When I first started doing this I talked to several people from companies that supply the salts. They all stresses the importance of the bath being at a rolling boil at 285 deg. and maintaining that temp.

                    You don't need a pressure pot to reach 285 boiling point. The salts raise the boiling point. Approx 8 Lbs of salts per gallon, from what I remember.

                    I never liked oil blackening.... the temps needed for that can start to mess with the hardness of your parts. The clean up is messy and the stuff flakes off too easy.

                    You can try cold blue just to see what happens. That's a good test to see if the part will take to hot blue. I do it on sometimes if I have something I'm not sure of.

                    Most recently were some screws. They wouldn't take to cold blue, then I realized that they were hard chromed....... a quick dip in the muriatic acid took care of that.
                    You can also try rust bluing..... it's a repetitive process I'm not crazy about it.

                    The brown coating is typical.... I get that most of the time. I think that comes from pulling the parts out of the hot bath through the surface scum.
                    Most of it goes away with the cold water rinse and the dip in the water displacing oil. Any traces wipe right off.


                    JL................
                    Last edited by JoeLee; 09-25-2020, 04:13 PM.

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                    • #40
                      The acid wash took off the black spot right away, again. Cleaned off the part, acid washed it again. It is currently in a new batch of potassium nitrate solution, this time mixed with condensed water (same as goes into the battery bank).

                      When thinking about temps etc, remember, this is not the NaOH solution, but the "markx method" from the link. It will be different from your method, your results. timing, etc will not apply directly, and per the info in the link, the 285 F is not needed.

                      Cold blue is worthless, in general, it wipes off pretty easily, at least it has for me, although I did not do the bluing.

                      As for the oil, you can harden the parts in the oil, and get the same result. No need to anneal the parts in the process.

                      O1 parts, I heat to red-orange and dump in. Out they come black, and it is a tough coating. A2 parts I let cool to just below glowing, and then dump in. They also come out hard, and black.

                      My input to this process has been moved to the "black oxide experiment" thread in which markx first explained it.
                      Last edited by J Tiers; 09-26-2020, 04:18 PM.
                      1601 2137 5683 1002 1437

                      Keep eye on ball.
                      Hashim Khan

                      If you look closely at a digital signal, you find out it is really analog......

                      Comment


                      • #41
                        Originally posted by tlfamm View Post

                        Nobody has knocked yet ...
                        That happens when you add item 2. XXX gallons Diesel fuel.

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