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  1. #31
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    Sorry Bob I must be thicker than usual tonight

    "Magnetite is moderately more protective against rust than plain iron and especially but it wear off and will still eventually convert to rust."

    "Magnetite is moderately more protective against rust than "regular orange rust" and especially but it wear off and will still eventually convert to rust."

    Still not getting it

    Paying attention because I want to try it. You know who's getting the blame if it doesn't work


    Stuart

  2. #32
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    Quote Originally Posted by Stustoys View Post
    Sorry Bob I must be thicker than usual tonight

    "Magnetite is moderately more protective against rust than plain iron and especially but it wear off and will still eventually convert to rust."

    "Magnetite is moderately more protective against rust than "regular orange rust" and especially but it wear off and will still eventually convert to rust."

    Still not getting it

    Paying attention because I want to try it. You know who's getting the blame if it doesn't work


    Stuart
    you might be thick so i must be jungle thick n dense

    when you figure out the vest way Stuart let me know...

  3. #33
    BobL is online now Member: Blue and white apron brigade
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    OK There are a number of possibilities to start with to guard against a (red/orange) rusted object form more rusting.

    1) remove old rust i.e. get back to Plain-raw iron

    2) Leave the iron rusty with orange/red oxide

    3) convert the r
    rusty with orange/red oxide to black oxide

    4) coatings and other conversions

    etc

    Of the first three, 3) is much better than the other two and the least effective is to leave the rust there - a rusted object has a greater surface area exposed and being more porous stays wet for longer hence rusts quicker than removing the rust and getting back to a flat dry surface.



  4. #34
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    So Bob, if you just boiled a red/orange rusted item in distilled water, would that be enough to convert to black rust? (as per post 28).
    From what I've read so far it seems to me that the the fuming is to establish a uniform coat of rust on the steel, so if it is there already?
    Michael

  5. #35
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Michael G View Post
    So Bob, if you just boiled a red/orange rusted item in distilled water, would that be enough to convert to black rust? (as per post 28).
    From what I've read so far it seems to me that the the fuming is to establish a uniform coat of rust on the steel, so if it is there already?
    Michael
    You are correct about the fuming being to establish a uniform coat of rust on the steel - but as important is that it is a THIN and smooth coating bonded to the base metal.
    Only a thin outer layer of red rust is converted by the boiling, so if the red rust layer is too thick it won't convert and it leaves a irregular layer of black oxide over the remaining unconverted rust which is porous and relatively un-protective.

    Remember once the water converts the outer layers of red to black oxide you end up rubbing most (99%) of the black oxide off so only the layer bonded closest to the metal remains. If that layer is not bonded to the metal it will bonded to underlaying red rust which is not a strong bond and will come off - if not now then later.

    Best (i.e. longest lasting) results are obtained with the smoothest surfaces since this can produce the thinnest layers.

    It's tempting to let the fumes rust the metal for longer to form thicker coatings of red rust.
    When I have done this the result was a thicker patchy layer of rust and resulting soot most of which come off but leaves a more patchy finish - more, shorter exposures, will be better than a fewer longer fuming exposures.

    When the weather is hot a 4-6 hour fume exposure is plenty. when its colder I use 8-10 hours. The worst finish was when I accidentally left something for 24 hours and the resulting coating was rough and irregular. If this happens early the resulting top layers will get increasingly rougher. If it happens in the second last or last pass it will still be protective but just may not look as as good.
    If this happens in the first 3-4 passes I recommend going back to bare metal and starting again

    In general the coatings on scotchbrite (matt) finished steel have not been as good as buffed to a mirror finish steel.

  6. #36
    BobL is online now Member: Blue and white apron brigade
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    Here's some pics after the final pass (9 passes in all) through the fuming tank and a bath in warm engine oil..
    The final pass included an accidental 24 hour fume in the fuming tank.
    This has resulted in a rougher finish but I'm not that concerned about these pieces having a real fancy finish as long as they are reasonably well protected.

    Photographic black things at night is difficult at the best of times but it is what it is.

    This is with led fluoro lighting - it's hard to see much on these surfaces as they are too dark.
    The glint you can see is a tiny bit of remaining oil


    Now with flash only
    You can see a bit clearer that they have a matt finish


    Here are the pieces all assembled into the bearing housing.
    For comparison the surrounding steel has two coats of matt epoxy-enamel black


    In this one I have pushed the exposure in Photoshop so you can more easily .see the rougher texture on the edges - its nowhere near as bad as it looks


    For comparison purposes here is the bluing of the small rotary table mounting plate and tool post I made a year or so back.
    This had 10 passes though the tank.


    .
    Attached Images Attached Images

  7. #37
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    Quote Originally Posted by BobL View Post
    You are correct about the fuming being to establish a uniform coat of rust on the steel - but as important is that it is a THIN and smooth coating bonded to the base metal.
    Only a thin outer layer of red rust is converted by the boiling, so if the red rust layer is too thick it won't convert and it leaves a irregular layer of black oxide over the remaining unconverted rust which is porous and relatively un-protective.
    I read all this information with great interest, and you seem to know a lot about it. You are undoubtedly right about more thin layers instead of one thick, but I can't understand what happens when you repeat the fuming/boiling several times. Wouldn't that form a thick layer also? (be it more uniform) that would be polished off? Reading the previous posts I assume not, but can you explain what happens?

    Peter

  8. #38
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by WoodBee2 View Post
    I read all this information with great interest, and you seem to know a lot about it.
    Don't be fooled by appearances. I have undertaken the process ~7 times in ~3 years and during that time blued/blackened maybe ~30 pieces.
    What I do know something about is inorganic chemistry as it used to be part of my day job but I'm not a corrosion expert.
    Corrosion science is very specialised and as complicated as or maybe more complicated than metallurgy.
    However, I can read and mostly understand scientific papers on corrosion.

    You are undoubtedly right about more thin layers instead of one thick, but I can't understand what happens when you repeat the fuming/boiling several times. Wouldn't that form a thick layer also? (be it more uniform) that would be polished off? Reading the previous posts I assume not, but can you explain what happens?
    The soot formation only forms where there is red rust.

    However, the red rust layer formed is not uniform either, instead it consists of a very thin layer over most of the metal and then patches of mounds, lumps, bumps and other structures most of which are fragile and porous. Provided all these red rust structures are thin enough they will be converted to black oxide but the fragile rust also becomes the soot which must be rubbed off to allow the fumes to get access to the untreated metal underneath.

    The soot comes off easily but the very thin layer of black oxide that is hard bonded to the metal and to itself is much harder to remove. In the first couple of passes, after removal of the soot the amount of black oxide that remains hard bonded to the metal is so thin and so sparse that the metal may only look like a dark grey.

    *********************************************************************

    If you want to know more read on
    OK lets take a step back and try to understand rusting.

    The simple view about rust formation is that air (oxygen) attacks the surface directly and eats holes in metal.
    Iron that has been kept away from water (including any condensation from humid air) can stay rust free for years and when it does rust it does not rust anywhere near fast forming a smooth layer - this is rare because there is always water in the atmosphere.

    What really speeds up corrosion is water, even the small amount in dry air is enough. When water droplets condense on cold iron the water already has dissolved oxygen in it and this is much more reactive than oxygen gas in the air. The dissolved O attacks the iron more on some places on the iron surface than others and forms an iron rich solution in the water drop.
    When the iron oxidises into the water it releases electrons into the metal which move to other local parts of the metal forming a slightly reducing environment in that area which pulls some of the iron out of the water droplet. This is why you get pitting, on some parts of the metal surface and in others you get mounds.

    This is a picture of bare steel left outside out of the rain - note the patchiness of the rust.



    Here is a schematic rom http://chemwiki.ucdavis.edu/Analytic...dies/Corrosion of what happens

    Because of the water, and that oxygen from the air can continually dissolve into the water, the small amount of reduced iron also deposits large variable amounts of iron oxides and water (embedded in the solid structure) which is what rust is and that is why it is rarely a uniform colour. It's not really a well defined material and is not considered a material at all in a chemical sense, instead it's considered a solid mixture. The deposit is loosely bound to the metal and unlike some other metal oxide layers does not form a barrier against further corrosion at this is why rust is so friable.

    Now what you don't want with metal bluing is any visible pitting or for the layer of rust to build up into large lumps which is happens when the metal is exposed to the acids for too long.
    You want the pits and the deposition spots to be so tiny as to be to be invisible and so all the red iron oxides to be converted to the black iron oxides. If the lumps are too big the red oxides will not be converted into black oxides and the surface will not be as strong as a solid black oxide only layer. What happens after boiling and when the soot is removed is you can reduce the high points but the pits generally retain some soot which is not desirable.

    I have never hear of this but I reckon that the brown hues sometimes seen during metal bluing is due to incomplete reduction of the red to the black rust. A very small amount of red rust inside the black rust can probably be tolerated.

    In my last pass on the parts I blued in this thread I did leave the parts too long in the fuming chamber and there were larger patches of rust formed.
    To show this effect I pushed the exposure in Photoshop in the picture below to show the speckled outer edges of these discs.
    The highllghts you see are not shiny metal but the polished tops of the converted or black oxide mounds that are reflecting the flash compared to the surrounding darker areas.

    This is why if you want a smooth finish, starting with mirror finish is essential because it's all downhill from then on.

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  9. #39
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    Hi Bob,
    I have been on holiday for a while, but have just read your thorough but understandable (to me) explanation. Thank you very much for the effort to write this all down!

    Peter

  10. #40
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    Quote Originally Posted by BobL View Post
    For Concentrated HCl I used Diggers Spiirts of Salts from Bunnings.
    Nitric acid is not so easy to get but Sulphuric acid can be substituted for nitric..

    Diluter forms will also work but take longer although some reduction in time can be achieved by then using a smaller chamber/
    Hi Bob,

    Bunnings dont seem to have Diggers anymore. They have Chemtech brick and tile cleaner, 95g/L Sulfamic acid and 53g/L Hydrochloric acid. Is that acceptable?

    Thank you.

    Stuart

    p.s. the funny thing is I have a blacking kit in the shed I havent even tried yet

  11. #41
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Hi Bob,

    Bunnings dont seem to have Diggers anymore. They have Chemtech brick and tile cleaner, 95g/L Sulfamic acid and 53g/L Hydrochloric acid. Is that acceptable?

    Thank you.

    Stuart

    p.s. the funny thing is I have a blacking kit in the shed I havent even tried yet
    Sulfamic is probably not oxidising enough.

    What about this mob.
    http://www.anpros.com.au/contact-us/

  12. #42
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    Quote Originally Posted by BobL View Post
    Sulfamic is probably not oxidising enough.

    What about this mob.
    http://www.anpros.com.au/contact-us/
    Considering they're about a 10 minute walk from my place they will do just nicely. Thank you.
    Don't they have lots of nice stuff! Though it is tempting to buy everything 2.5L at a time (which granted would be more then a little silly)

    Stuart

  13. #43
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Considering they're about a 10 minute walk from my place they will do just nicely. Thank you.
    Don't they have lots of nice stuff! Though it is tempting to buy everything 2.5L at a time (which granted would be more then a little silly)

    Stuart
    It's not worth keeping large amounts of nasty stuff in a domestic environment. Before we had an accountable acid disposal system at Uni I acquired a 20L carboy of used high purity aqua-regia. When I say used it was used, it had been used for cleaning labware that was already way cleaner than would be the case in most labs. It was going to be disposed of so I grabbed it. I used some of it in a plastic bucket to dissolve Zinc plating off some steel pipe - veritable little volcano that turned out to be leaving a 5ft clean ring of brickwork on the back pergola paving. When the black plastic 20L carboy started to blister I got worried and I didn't want to keep it in the shed or under the house for obvious reasons so it lived on the back veranda for a while - bit of risk when kids came over to play. I did some steel etching with it - nothing fancy and not that good either. With summer coming I transferred half a litre to an FEP teflon container and used the rest to clean the remainder of the pergola and driveway brick paving. It worked great - killed all the weeds, moss etc and nothing grew in between the bricks for a couple of years.

  14. #44
    BobL is online now Member: Blue and white apron brigade
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    Although this is an old thread, as it already contains a heap of info about cold fume rust bluing, rather than start a new thread I will append info about more fume bluing experiments I have been conducting in the last few days.

    One thing that would be handy is not to have to wait for so many days to arrive at a finished blued product. Normally this does not worry me as I already work around many projects at the same time but I am aware that this does involve a chamber containing smaller containers of exposed concentrated acids involved and simply I would like to minimise the time over which this exposure occurs. Knocking over the chamber and allowing the acids to mix would be most unpleasant as could generate Chlorine gas.

    There are of course many commercial bluing agents available, and other ways of bluing like hot bluing, but rather than purchase new chemicals and as I already have a fume tank/chamber on hand I just wanted to see if I could speed up the process. Besides, cold fume bluing is still considered the best rust resistant form of blue available although hot bluing produces the most wear resistant bluing.

    One thing I have noticed, and already mentioned this in previous posts, is that temperature plays a big part in how quickly the red rust develops inside the tank. When the weather is hot, a 4-6 hour fume exposure is plenty. when its colder I will expose for 8-10 hours, and these last few days when its been 3-4º overnight I have exposing for 12-14 hours.

    So to speed things up especially on (colder days and nights) I made a up a warming plate a box made of MDF/galv sheet.
    The heat source is just an incandescent lamp controlled by a dimmer switch.
    The max temp differential (relative to the concrete floor of the shed) inside the bottom of the plastic tank is about 15ºC with a 25W incandescent globe and 30ºC with a 50W halogen globe so it could probably handle a 60W globe OK.
    If you notice there are small rectangular holes near the corners of the box that do allow some hot air to escape - there are two more at the back behind the tank and I can get the box hotter by blocking some these holes.
    WarmTank.jpg

    Below is what I get after just two passes through the tank.
    One pass was at 15 degrees (25W globe) above ambient overnight, and one pass at 30º above ambient (50W globe) for just 6 hours.
    2passes.jpg

    The surface of these pieces are not initially polished - they are just various handles from my trigrinder stand - so I am not expecting too much in terms of smoothness.

    Observations"
    The amount and thickness of the black soot developed per pass is greater using the warming plate than that produced at cooler ambient temperatures even over a longer period. This is consistent with a thicker black soot layer produce on warm/hot days.
    Although most of the extra black soot comes off, the remaining layer of black oxide is much thicker per pass - again consistent with previous experience of just exposing the objects in a colder tank for longer.
    The remaining black oxide layer seems a bit rougher that at lower temperates although some of this could be due to the surfaces not being that flash to sort with. Again constant with previous experience

    In the photo below I show an un-blued handle below and the top handle is what I normally see after 4 passes through the fume tank on cold days
    Bluing1.jpg

    So over all it seems like the warming plate does speed things up and the level of finish appears fine for rust control but number of exposures and exposure time may need to be tweaked to improve the finish.

    Perhaps more/shorter passes will produce a better finish so my next experiment is going to be 3 x 3 hour passes at 30º above ambient. I would like to be able to fit the whole process into one day or one 24 hour period.

    In another thread I refer to a "paint on" H2O2/NaCl rust bluing method - I will be trailing this method and reporting on it in this thread.

  15. #45
    BobL is online now Member: Blue and white apron brigade
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    Baby sitting duties today so no time for shed stuff during the day but this evening I finished the warmed fume bluing experiment I started above.

    The pieces below have had 3 passes through the warmed fume chamber.
    The 3rd pass produce very little red rust indicating that the black oxide developed during the first two passes was already covering almost all of the metal.
    In terms of looks, it's about equivalent to between 7 and 9 passes at ambient temperature so this is significantly faster.
    Given the average quality of the starting surfaces I am more than happy with this for protective purposes.
    Whether it actually does the deed long term, only time will tell.

    Trigrinderhandles.jpg

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