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So I tried out rust bluing

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  • #16
    Originally posted by MrWhoopee View Post
    So after reading this thread, I decided to give it another try. I used the peroxide/salt solution. I treated the parts a total of 4 cycles: rust in the solution, rinse with cold water, boil, then dry and brush the loose rust off with an old toothbrush. By the fourth treatment, the reaction became noticeably less vigorous. Before oiling, the color was more plumb brown than black. Here's the finished product, before and after oiling.

    .....
    Thanks for the good information. It does seem that "all rust is not created equal" when it comes to the process. Regular orange surface rust seems not to become black, while more tenacious red rust does. I assume both are Fe2O3, but they sure do not act the same.

    I will see if I can scare up any peroxide.... in these days it seems that it has vanished in the same way as hand sanitizer and toilet paper did..
    1601

    Keep eye on ball.
    Hashim Khan

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    • #17
      Hair bleaching products. I have some 12% Peroxide cream that I use for de-yellowing old plastics to make them look new again.

      Comment


      • #18
        Originally posted by J Tiers View Post



        I am just NOT into "checkbook machining", that should be fairly obvious from the various tooling projects I have posted or sent to the magazines..... so I have no issues trying 10 different methods. The point here was to try the methods. I'd do hot bluing if I had the AN.
        If you mean the classical hot bluing procedure with oversaturated lye and nitrate mix that liquefies at temperatures over the boiling point of water, then for this approach you really do not need AN. One of the procedures calls for mixing of AN and lye in the preparative stage and cooking it until no more ammonia gas evolves. In this step AN reacts with lye (sodium hydroxide) to form sodium nitrate and expels ammonia gas:

        NH4NO3 + NaOH -> NaNO3 + NH3 + H2O

        Lye is taken in excess and after the AN has reacted you are left with a mix of sodium nitrate and lye in precalculated ratio. That is the classical hot bluing salt mix. For practical purposes it is way quicker and more reasonable to start with sodium nitrate, lye and water. The end result is the same, but you do not have to deal with the reaction stage that evolves noxious ammonia gas and takes sometimes hours to complete. I really do not know why it was proposed to start with AN and lye for this approach.....perhaps at the time of writeup these two ingredients were the cheapest and most available. But at these times AN is a rare commodity.
        So if you have access to sodium nitrate then you can just start with that for the hot bluing. For practical purposes I do not see why potassium nitrate should not work in this combination. There might be some variations in resulting coloration of coating with using potassium nitrate, but in essence it should work.

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        • #19
          i whish somebody proficient in chemistry would chime in.

          there seem to be 5 types or anhydrous oxide ( all black?) and 10 types of hydrated oxide (yellow-red-brown). there is green and blue rust. also there are reactive types (black?) and free types that can be converted. the colour of the free types seems to depend on how much moisture was present. i believe the issue is that a substance with the same formula can be present in diffent forms like soot and diamond.

          it would be imperative to know, what we are looking for to get the desired coating (mechanically resistant, also resists acids and bases and is non conductive). e.g. ferrous-hydroxide [Fe(OH)2] is black and converts in water to black magnetite ("black oxide", "Fe3O4", really a mixture of FeO and Fe2O3). also: what mixture of these are we looking for? where woud ferrous-hydroxide come from? there is a lot going on, e.g: FeSO4 + 2NaOH = Na2SO4 + Fe(OH)2.

          two thought:

          1) find how the pigment "black oxide" is produced. but is it what makes up the desired coating?
          2) understand conversion coatings and how "red rust" is chemically converted to "black rust".

          black rust can be of such "high quality" that its a considerable problem for railways. its an isolator and doesnt get destroyed by the wheels.
          Last edited by dian; 10-15-2020, 04:47 AM.

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          • #20
            Originally posted by DennisCA View Post
            Hair bleaching products. I have some 12% Peroxide cream that I use for de-yellowing old plastics to make them look new again.
            This is something I would like to find out more about. I've noticed that most computer cases and my copier which both have the same off white plastic cases tend to yellow over time, especially if they are exposed to direct sunlight. I wasn't aware of any way to remove the discoloration.

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

            Comment


            • #21
              Originally posted by dian View Post
              i whish somebody proficient in chemistry would chime in.

              there seem to be 5 types or anhydrous oxide ( all black?) and 10 types of hydrated oxide (yellow-red-brown). there is green and blue rust. also there are reactive types (black?) and free types that can be converted. the colour of the free types seems to depend on how much moisture was present. i believe the issue is that a substance with the same formula can be present in diffent forms like soot and diamond.

              it would be imperative to know, what we are looking for to get the desired coating (mechanically resistant, also resists acids and bases and is non conductive). e.g. ferrous-hydroxide [Fe(OH)2] is black and converts in water to black magnetite ("black oxide", "Fe3O4", really a mixture of FeO and Fe2O3). also: what mixture of these are we looking for? where woud ferrous-hydroxide come from? there is a lot going on, e.g: FeSO4 + 2NaOH = Na2SO4 + Fe(OH)2.

              two thought:

              1) find how the pigment "black oxide" is produced. but is it what makes up the desired coating?
              2) understand conversion coatings and how "red rust" is chemically converted to "black rust".

              black rust can be of such "high quality" that its a considerable problem for railways. its an isolator and doesnt get destroyed by the wheels.
              Iron compound chemistry is rather versatile and quite complicated.....apart from the numerous oxides and hydroxides there also are oxide-hydroxide compounds of iron (goethite, schwertmannite, ferrihydrite e.g.). Some of these can include other ions (chloride, sulfate) in their composition giving different coloration (green rust e.g.). In short there is nothing straightforward about the mechanisms that create or sustain these compounds.
              In general magnetite is formed when both iron (II)- ferrous and iron(III)- ferric ions are present in the same system. Ferrous ions are more stable in acidic media and when strong reducing agents are present. Otherwise they shall be converted to ferric ions by ambient oxygen or other oxydising agents in the system. If a mix of ferric and ferrous is brought from acidic conditions to neutral and basic, the ions tend to percipitate as hydroxides/oxides and merge into magnetite finally. That is how magnetite powder is usually produced: by mixing ferric and ferrous soluble salt solutions together (chlorides e.g.) and then raising the pH of the combined solution by adding a base (ammonia solution, lye). The iron ions form insoluble oxides and merge into magnetite in the end as a result of this step.

              Something similar happens in the blackening baths, but with the aid of the metallic surface of the part being covered. The exposed iron acts as both a source for the ferric ions (blackening baths are of oxydising nature, thus ferrous ions are not stable in the solution) and as a reducing agent for them near the metal surface. Metallic iron is a strong reducing agent that is able to turn ferric ions to ferrous and thus arises a mix of those on and near the surface of the part to be coated. This mix shall be converted to magnetite that deposits itself onto the steel surface. If no more surface is exposed, the process is effectively at an end and further magnetite can not be formed.

              During rust bluing we create the iron compounds and ions on the steel part by corroding it with an acidic solution and forming acidic salts of the ferric and ferrous kind together with the oxides and hydroxides. These recombine to magnetite during the boiling phase as the pH shall rise towards neutral in the hot water and these conditions do not favor the presence of soluble iron salts. So they take the form of more stable oxides.

              That explanation is of course rather oversimplified and does not explain the numerous nuances that additives or contaminants (also alloying elements in the steel) can inflict upon the process. Either enabling it to proceed faster or on the contrary stopping it dead as can happen with some alloys and parts that were mentioned in previous replies....

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              • #22
                Originally posted by JoeLee View Post
                This is something I would like to find out more about. I've noticed that most computer cases and my copier which both have the same off white plastic cases tend to yellow over time, especially if they are exposed to direct sunlight. I wasn't aware of any way to remove the discoloration.

                JL.............
                https://hackaday.com/2017/11/03/yell...-of-a-sunburn/

                Comment


                • #23
                  great write up, mark.

                  1) what can be done to assure a sufficient supply of suitable ferric oxide (hematite)? there obviosly are different oxides that form, resulting in the spectrum of colours. is the colour a dependable criterium? yellow is no good, red is what we want, or is it brown?

                  2) from what you say i understand the boiling solution (water) should be ph neutral. yes? can you elaborate on what "additives" in the solution would hinder/promote magnetite formation? (unless you were talking about additives in the steel.)

                  and an idea: if you were to purchase red or/and brown iron pigment, mixed it up in water and let is simmer with steel, would anything happen?
                  Last edited by dian; 10-15-2020, 11:29 AM.

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                  • #24
                    Originally posted by JoeLee View Post
                    This is something I would like to find out more about. I've noticed that most computer cases and my copier which both have the same off white plastic cases tend to yellow over time, especially if they are exposed to direct sunlight. I wasn't aware of any way to remove the discoloration.

                    JL.............
                    I take the piece I want to bleach and brush on the cream, then I wrap it with plastic wrap to prevent evaporation. Then I put it in the sun, or if you want to, in a box under a UV light. The UV light with the peroxide does the bleaching.

                    Comment


                    • #25
                      Originally posted by dian View Post
                      great write up, mark.

                      1) what can be done to assure a sufficient supply of suitable ferric oxide (hematite)? there obviosly are different oxides that form, resulting in the spectrum of colours. is the colour a dependable criterium? yellow is no good, red is what we want, or is it brown?

                      2) from what you say i understand the boiling solution (water) should be ph neutral. yes? can you elaborate on what "additives" in the solution would hinder/promote magnetite formation? (unless you were talking about additives in the steel.)

                      and an idea: if you were to purchase red or/and brown iron pigment, mixed it up in water and let is simmer with steel, would anything happen?
                      1) Colour is in general not a dependable criterion as different rusting solutions tend to produce differently colored deposits. I'm referring to the rusting solutions used in the "rust bluing" technique prior to the boiling step. Salt+peroxide usually produce a red deposit, whereas ferric/ferrous nitrate solutions tend to dwell into the yellowish end. Both are able to yield a quality black effect in the end. Trial and error type of work truly....

                      2) Hot water acts as a dilutant and suddenly shifts the background system conditions to a state where stable oxides are favored, as soluble iron salts are usually not able to exist under alkaline or near neutral pH and form hydroxides or oxides, especially in dilute solutions. In fact alkalinity is a powerful inhibitor of steel corrosion. That's why rebar does not corrode in concrete until the slightly acidic carbon dioxide from ambient air has saturated the structure and rendered the alkalinity of concrete ineffective and near neutral. That process can take decades.
                      Additives are a whole different fairy tale. Again everything depends on what method of blackening we are talking about....for rust bluing I really can not comment, but for hot bluing a whole myriade exist with sodium nitrite (NaNO2 : also used as a preservative for curing meat) being quite common. Also compounds of titanium, molybdenum and several rare earth metals are often used as a sort of "catalyst". For the "intermediate hot" dilute AN solution method I've found oxyhalogen salts like chlorates and perchlorates to have a positive effect on the speed of coating, when used in controlled small amounts. Though if overdosed they quickly turn the blackening bath inert. As to exactly why that happens is a mystery to me.....I suspect one could devote an entire lifetime to finding out why and might still be left clueless in he end. And the same could be said about the alloying elements in the steel itself.
                      As for trying to force a commercial pigment type oxide mix to stick onto steel surface by supending it in water is in my opinion a lost cause. But I've been known to be wrong before, so by all means do try it out
                      I do not intend to crush any hopes, but the pigment powders are nearly not fine enough to achieve intimate contact with steel surface for a successful deposition reaction. They agglomerate and become rather inactive upon drying into pigment form. That process is irreversible for practical purposes. Only something that is formed directly on the steel surface either by previous intentional etching or via the action of the blackening bath constituents is able to be deposited successfully as adherent black oxide.

                      Comment


                      • #26
                        thank you. so there is no point in trying to condition the water homehow, right?

                        i can report the following:

                        i had three samples of bright sheet metal sitting in solutions for two months now: in peroxid, salt and salt plus vinegar. they were all black. the first and second had black particles in the solution, the third had red ones. the second and third black coating rubbed off with a tooth brush (one side). the peroxide didnt. i put them into simering water and added two other pieces with reddish rust on them. after two hours all pieces were clean, not bright but light grey, except the peroxide piece that had a nice smooth black coating that doesnt rub off with a kitchen sponge. its very thin but i can see how three or four of these coats would yield a satisfactory result.

                        so im not very surprised jt's piece doesnt take the coating.

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                        • #27
                          Originally posted by dian View Post
                          .........

                          so im not very surprised jt's piece doesnt take the coating.
                          It's black in places. Just not all over. I assume the alloy is at least somewhat even throughout.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #28
                            Originally posted by J Tiers View Post

                            Comes from thinking like an insurance person. ..
                            Jerry, I am starting to think like an insurance person too.
                            All this home shop chemistry sounds dangerous.
                            Do you have a permit to operate a chemistry laboratory?
                            Do you have approved methods for storage of these chemicals you are using?
                            Do you have a mitigation plan if a chemical breech or spill should occur?
                            Does the fire department know about these chemicals?
                            Does your insurance company now about these chemicals?
                            Are you boiling solutions with these chemicals?
                            If these are iron base they might be heavy metals classified and might require additional permits.
                            Boiling chemicals classified as hazardous could come under the jurisdiction of processing hazardous waste.
                            This will require another permit and subsequent followup monitoring by local, state, and possible federal agencies.
                            Boiling means evaporation, would would require a clean air permit. You would need fume extraction equipment
                            installed my a licensed contractor and inspected by an agent that has their authority up to date and on file, and
                            accessible to be inspected by the public record. If you are not evaporating these chemicals when boiling, they
                            would have to be contained by a reclassifier vessel and the precipitate captured by an approved vessel that is
                            certified and inspected to maintain containment of said chemicals on a state recommended cyclical basis.
                            How are you disposing of used chemicals? Depending on the toxicity and the bylaws you local, state and
                            federal jurisdiction, you might require additional permitting. To assess the viability of applicability of the
                            reliant toxicity protocol, you may be subject to fees to cover the costs of contracting an independent laboratory
                            to assess and classify the chemicals you are looking to dispose of. Also depending on the hazardous material
                            classification category that you fall into, you will also have to pay transportation fees to have a chemical storage tanker
                            truck transport them to a state regulated land fill disposal site. There are road taxes associated with truck transport
                            of your chemical on or over a public highway. There are also independent inspectors that must visually verify that
                            the truck used for transport of your chemical waste was fully evacuated during the dumping and removal process.
                            There may be additional fees to have the tank steam cleaned if your chemicals are of the reagent type, that might
                            cause lingering problems of chemical residue for the tank truck used to transport your chemicals to the disposal site.
                            There are also long term disposal site maintenance fees, unless you can qualify as gross polluter, toy might qualify
                            as a super fund site containment funding recipient, whereas the taxpayer will pay to supervise the storage of your
                            chemical waste as it is entombed for internment. Are you under a liability contract with an home owners association?
                            You might have a legal obligation to disclose to them if you are doing any chemical processing, and may have to
                            disclose any chemical waste stored on site. Are you in compliance with all this?

                            --Doozer


                            DZER

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                            • #29
                              Doozer -- you do realize that I live less than a mile from Love Canal? Your post gave me a smile

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                              • #30
                                Doozer, if you had any idea of what is present on the various properties I own, even YOU would have a hissy fit. But I am not particularly concerned. My advice to you is not to "go there" about the matter, you just do not know who/what you are dealing with.
                                1601

                                Keep eye on ball.
                                Hashim Khan

                                Comment

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