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Thread: Black oxide experiment

  1. #11
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    Quote Originally Posted by DennisCA View Post
    We're talking the usual hot bluing usually applied to guns now. In that case KNO3, potassium nitrate works as well. I've used it to blue firearms.

    Another method is fume bluing, suspend the clean degreased parts in a tight container with some acid (hydrochloric) and let them rust, then take them out and clean off the rust with a very fine steel brush, then boil the parts. For firearms this can be repeated for a deeper finish, for parts just one pass might be enough.
    Even potassium nitrate is difficult to get nowadays. And it requires? the strongly caustic&hot lye bath.. not something you want to cook in kitchen.
    Fume bluing.. too much hassle unless you are into antique firearms and what I have seen it's not as durable as hot bluing.
    "real" AN-based hot "blackening" is supposed to be more durable than KNO3+lye hot blue.

  2. #12
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    I edited my post to clarify. I get KNO3 from my parents who are farmers.

    Fume bluing is the same process as rust bluing, different application, it is considered more durable than hot caustic bluing.

  3. #13
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    How do you dispose of the liquid waste? What is it, and how toxic is it?

  4. #14
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    Quote Originally Posted by Glug View Post
    How do you dispose of the liquid waste? What is it, and how toxic is it?
    Should be really mild and easy to dispose compared to "normal" lye hot bluing bath.
    Ammonium nitrate is usable as lawn fertilizer and some iron oxides won't matter in that use.
    Hexavalent chromium would be the only potential skeleton in this closet.. no idea if it can form in the process or not.

  5. #15

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    Quote Originally Posted by MattiJ View Post
    Should be really mild and easy to dispose compared to "normal" lye hot bluing bath.
    Ammonium nitrate is usable as lawn fertilizer and some iron oxides won't matter in that use.
    Hexavalent chromium would be the only potential skeleton in this closet.. no idea if it can form in the process or not.
    One does not need to dispose of the bath after using.....essentially the ingredients do not spoil or become depleted in the process (apart from water being evaporated), but rather work like a chemical pump to convert the surface layer of iron into magnetite. I've been using the same solution for dozens of times and it still works pretty much the same. If one does not add any accelerants to the bath then by all means it can be used to fertilize the lawn around the workshop. That's what the initial purpose of the main ingredient is

    As for Cr(VI) I really doubt that it shall form or remain stable in this kind of environment. Hexavalent chromium is a strong oxydiser and there are too many reductive species in the bath that would react with it. First of all the iron compounds that are initially formed in the bath when metal surface is contacted with the solution are of ferrous nature :Fe(II)+2. These are known and effective hexavalent chromium reducers. E.g. ferrous compounds like ferrous sulfate are added to cement and cementitious mortars for chromium reducing purposes. I know because I formulate cementitious mortars as a day job

  6. #16
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    Quote Originally Posted by markx View Post
    One does not need to dispose of the bath after using.....
    That would be another bonus. And it should store nicely in a plastic bottle when you don't need it. Traditional lye bluing solution is creeping up the container walls in storage, and generally makes a mess. Cannot be stored in plastic bottles because its either too hot or too solid. .

    I have been using phosphorous acid parkerizing/phosphating solution for some of my parts but the solution is sort of single-use only and seem to be bit tricky to get right in home brew chem shop.

    Only problem I see is that I have to start with Haber-Bosch process nowadays to get AN
    Last edited by MattiJ; 11-15-2018 at 12:33 PM.

  7. #17
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    Quote Originally Posted by MattiJ View Post
    I have been using phosphorous acid parkerizing/phosphating solution for some of my parts but the solution is sort of single-use only and seem to be bit tricky to get right in home brew chem shop.
    I don't know about phosphorous parkerizing, but manganese parkerizing solution is definitely not single use by any means, and is very easy to do at home. I've been using the same solution for ~4 years now, and the previous batch for ~8 years before that. It's a very similar process to what the OP shows, except lower temp and the need to abrasive blast the parts before hand.

    If you're having trouble getting it to work, you've probably got the solution too hot. Use a thermometer, and err on the cooler side.

  8. #18
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    Quote Originally Posted by Yondering View Post
    I don't know about phosphorous parkerizing, but manganese parkerizing solution is definitely not single use by any means, and is very easy to do at home. I've been using the same solution for ~4 years now, and the previous batch for ~8 years before that. It's a very similar process to what the OP shows, except lower temp and the need to abrasive blast the parts before hand.

    If you're having trouble getting it to work, you've probably got the solution too hot. Use a thermometer, and err on the cooler side.
    Manganese parkerizing the name I was after. Been bit of lottery how it works.
    I don't have abrasive blasting at hand so that could be one reason to fail..

    Do you use homebrew manganese parkerizing solution or ready one from Brownels or similar?

  9. #19
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    Quote Originally Posted by markx View Post
    ... Ammonium nitrate : 10g
    Distilled water : 1000ml (1L) ...

    ... The bath operates with ferrous alloys at boiling point of water or slightly lower (95-100C) due to the dilute solutions and has no caustic components that can cause chemical burn or damage the surroundings when spilled. ...
    What kind of container is suitable for heating? SS, aluminum, other?

  10. #20

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    Quote Originally Posted by RichR View Post
    What kind of container is suitable for heating? SS, aluminum, other?
    Stainless steel is best. Aluminium could theoretically be used, but I have not tried it. A steel vessel could be used, it will be coated on the inside with black oxide and become inert in terms of further involvement in the coating process. Galvanised steel and copper or zinc alloys must be avoided, they shall contaminate and render the bath inert. Also galvanised parts that have been stripped from the metal coating do not react well in the bath. Oxide coating is uneven and very slow to develop....mostly of matte appearance and porous. Also do not store the bath solution in the metallic container, cold AN solutions are corrosive towards metals (except to stainless). Pour the bath into a plastic or glass vessel for storage between use. PET and PE vessels are ok to use for that purpose. The ferrous oxides shall precipitate to the bottom of the storage vessel and next time one can decant the clear solution off the precipitate for another round of use. Or filter the sediment off separately. I never bothered as it shall form again upon every use of the solution.

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