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  • Originally posted by reggie_obe View Post

    For the blackening process, it has to be ammonium nitrate, just a high nitrate fertilizer?
    At least for the ”lye free” recipe that we are interested in here it has to be AN, not just any nitrogen fertilizer.
    Location: Helsinki, Finland, Europe

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    • Originally posted by MattiJ View Post
      Looks like Franz(c) packed his bags and left us with some broken quotes.
      Was kind expecting him get banned or something soon, sounded like random ranting of PM-Monarchist
      huh, how about that. He was very much like Thermite/ Monarchist - some pearls of wisdom, but an awful lot of empty oysters to sift through to find them.

      couldn't find any UAN on Lowes/ HD websites, though most likely that's because their websites completely suck. Guess I'll have to get off my butt and go and have a look in person.

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      • Originally posted by mattthemuppet View Post
        ...couldn't find any UAN on Lowes/ HD websites, though most likely that's because their websites completely suck. Guess I'll have to get off my butt and go and have a look in person.
        Don't waste your time. Not only do their websites suck, but so do their stores.

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        • yeah, hard to disagree with that. I do enjoy rooting through their recycled battery bins though, sometimes find some jems there

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          • woohoo! Was chatting with my chem buddy (asked him if he wanted my crystalised urea) and he said they should have ammonium nitrate in the stock room. 5 min lathe I have 20g of AN, plenty enough for the volumes I'll be working with. Might try it this weekend if I have time.

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            • all right! This worked a dream, thanks markx and everyone else. Even bought a stainless pot from the thrift store so my wife wouldn't kick my ar$e for spoiling hers

              before (top left holder has been cold blued)

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              cooking some steel soup
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              all done!
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              some splotchiness - I cleaned them with Dawn, but then handled them after (you can even see my finger prints on one). Next time I'll take the same cleaning approach as I do with anodising. Also should have removed some paint on the pieces that was there on the original 4x1x11" piece of steel as that caused a right mess.

              Anyway, happy as a clam. Now need to get my 3D printer set up in the garage and print some more holders for my holders!

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              • @ mattthemuppet:

                Looks like a good result - how long did you 'cook' the workpieces?

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                • If you see some splotchiness or spots forming then it is a good idea to fish the piece out of the solution, clean it under running water with a scotchbrite or abrasive dishwashing pad and put them back into the stew. The weakly adherent coat will be removed around the splotchy spots and fresh surface will coat over nicely. The abrasive pad is also a good indicator to the quality of the formed coating. If a correct black oxide has formed then the scrubbing shall not affect it.
                  Also one can redo the coating process if the result seems not satisfactory....just clean the oil (if it has been applied) with some solvent or dishwashing soap and stick the pieces back into the bath. I do not recall it happening that the coat was not improved by this method. In fact I've done the recoat without removing the oil on some noncritical pieces and it still seems to work just as good.
                  Watch out for any aluminium sticking onto steel surface prior to coating. If you used a cutting tool that had some aluminium sticking to it and it was trasferred to the workpiece while machining then the aluminium bearing spots will not cover and remain very visible. I've been unable to correct these even with extensive scrubbing and recoating attempts.

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                  • thank you Mark, that's a great tip, I'll remember that for the next time. These'll do just fine as they are, they'll get covered in oil and chips soon enough, but I'll give this a shot with the scissor knurler that's next on my list.

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                    • Carrying on with the experiment.

                      I had some odds and ends that I needed their own black oxide, so I used a really old technique for the procedure. It is "rust bluing" (it's really "rust blackening", but why quibble..). It can be easily done with materials probably in your house right now, or even just a quick trip to a store for the supplies. First, let me post pics of the results:


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                      Very minimal surface prep was done on these part, other than an acetone wipe down to remove any oil. I wore a nitrile glove when handling the parts as to not transfer any oil to them.

                      The procedure:

                      Pour a half-cup of H2O2 (hydrogen peroxide) in a non-metallic container.
                      Mix in approximately 2 tablespoons of regular NaCl (salt) until the salt is dissolved (mostly). You want a saturated solution, so if salt still remains after you have mixed for a minute or two, don't worry about the extra.

                      Brush this solution onto the metal and let it sit for more than 10 minutes. I don't think the time really matters, as the rust forms almost immediately.

                      In a large pot (I used stainless steel), bring about two quarts of water to a boil - I used regular tap water.

                      Drop the parts into the boiling water and boil for 10 minutes or more.

                      Remove the parts and let them dry, then repeat the process.

                      Every second or third time thru the process, brush your parts with a stainless steel brush to remove the black above the surface. This will seem like a "two steps forward, one step back" type of operation, but the black will continue to deepen on the surface of your part.

                      Continue to repeat the process until you get a black that you are happy with. I believe that these parts were done in six loops.

                      Once you have your black, coat the parts in oil (the oil really makes the black "pop").

                      Some things I learned:

                      1) Make sure your parts are dry BEFORE you put on the solution. The extra water just dilutes and weakens the solution.
                      2) You really DO have to card your parts (brush with the SS brush).
                      3) Get the surface appearance you want BEFORE you black. The black won't fix ugly, it will only make it black and ugly!
                      4) The two collet stop centers would NOT black - in fact, they wouldn't even RUST. They are supposed to be O1 rods, but act more like stainless.
                      5) The process is messy - the extra black oxide gets everywhere, especially your hands if you're not wearing a glove. It scrubs off, so if you do get messy, don't worry. The SS pot that I used has black splotches all over the bottom. It cleans off with an abrasive cleaner like AJAX or COMET.

                      This is supposed to be one of the most durable black oxides there are, because it is just a conversion of regular red rust Fe2O3 to black rust Fe3O4.

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                      • I can vouch for the peroxide-n-salt rust bluing, it works. Will say be careful not to get it on anything you care about. I inadvertently dumped it on a steel workbench once...

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                        • Just a note on this.

                          As far as I can see, potassium nitrate does not work at all in the process recommended in the OP.

                          I have tried this several times with a particular part, cleaning, acid washing, etc, using stump remover that has potassium nitrate. I am essentially unable to discover any change in the part. There "MAY" be a slight haze after 40 minutes boiling, but no real darkening.

                          It looks as if the ammonium nitrate is the required material (per the OP, I have not been able to try it), and the potassium nitrate (which I have tried multiple times) does not do it, or if it will, it takes many hours, perhaps 8 hours or more.

                          There is, of course, a chance that the potassium nitrate material I have is either degraded, or too dilute to work. However, it is presumably concentrated enough to supply oxidizer for burning out a tree stump down through the roots. I can up the concentration, although the OP suggests that with the ammonium nitrate the process becomes "unstable" (not sure what that means) at higher concentrations. He also suggests that the concentration is not critical below a certain mass ratio, which I am certainly below.

                          I wish I could compare the two, but, then, if I had the AN, presumably I could get the process working, and would not need to worry about the potassium nitrate.
                          Last edited by J Tiers; 09-26-2020, 11:42 AM.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • Here is the result after several hours in the boiling solution. I added more KNO3 "material" to the solution, probably an ounce or more in there now. There is some hint of a darkening, assuming it is not just scum from the solution.

                            So far no sign of a dark black coating.



                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • Another 2 hours, more concentration in bath, same result, almost no change. I'd post a pic but you'd think it was the same one.

                              Forget this, it's time for rust bluing, or the torch.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment


                              • Originally posted by J Tiers View Post
                                Just a note on this.

                                As far as I can see, potassium nitrate does not work at all in the process recommended in the OP.

                                I have tried this several times with a particular part, cleaning, acid washing, etc, using stump remover that has potassium nitrate. I am essentially unable to discover any change in the part. There "MAY" be a slight haze after 40 minutes boiling, but no real darkening.

                                It looks as if the ammonium nitrate is the required material (per the OP, I have not been able to try it), and the potassium nitrate (which I have tried multiple times) does not do it, or if it will, it takes many hours, perhaps 8 hours or more.

                                There is, of course, a chance that the potassium nitrate material I have is either degraded, or too dilute to work. However, it is presumably concentrated enough to supply oxidizer for burning out a tree stump down through the roots. I can up the concentration, although the OP suggests that with the ammonium nitrate the process becomes "unstable" (not sure what that means) at higher concentrations. He also suggests that the concentration is not critical below a certain mass ratio, which I am certainly below.

                                I wish I could compare the two, but, then, if I had the AN, presumably I could get the process working, and would not need to worry about the potassium nitrate.
                                You are correct.....potassium nitrate does not work for blackening of steel when used in this process. Nor does any other nitrate salt that I know of. Only AN creates acceptable coatings and it can not be substituted by another more readily available salt to achieve the same kind of outcome. There is a commercial fertilizer branded under "calcium nitrate", which in reality is a calcium ammonium nitrate double salt. That one sort of works on some steel grades as a substitute for AN, but results vary and coatings are not of high quality.

                                About the concentration and instability issues of AN that I mentioned in my first posts: at higher concentrations the AN solution works in unpredictable and unreliable ways as a blackening agent. The process takes longer, coatings can become uneven, porous and loose. On yet higher concentrations (like in the 30% by weight and upwards range) the AN solution acutally becomes corrosive towards steels, strips off any oxides and etches the surfaces to bare metal. I've used the effect on one occasion to strip off old BO coating from a set of bolts that I recoated afterwards. So less is clearly more in this particular case

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