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  1. #16
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    Quote Originally Posted by Russell Cook View Post
    Hi guys,

    Jill mentioned the black marks left after removing rust with acid looking terrible. I have also had this experience when using acetic acid rather than citric acid.

    Do the black marks have any effect on the function/condition of the tool, or is it just an aesthetic thing? If it's just aesthetic I can live with it
    Russell, I've found that the blackest stuff scrubs off with a plastic brush under water, which leaves a grey (fairly hard) residue. This appears to give some level of rust protection. It may be a substance called "Pearlite". It can be polished off with a wire brush if you want the tool to look better, or it can be left on for a little added protection.

    In using Citric, Acetic and Hydrochloric acids, I've always found the same residue present. I suspect that the black part is converted rust, and the grey underneath is converted steel.

    HTH
    Brett
    Regards, FenceFurniture

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  3. #17
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    A few misconceptions that need correcting in this thread

    Quote Originally Posted by FenceFurniture View Post
    It seems there are two ways of efficiently removing rust from tools, and both methods have their afficianados:
    1. Electrolysis
    2. Citric Acid
    There are many more of ways to remove acids that this.
    Your comparison of Electrolysis and CA is rather odd since Electrolysis is a process where as CA is an acidic product no different in it's behaviour regarding rust to vinegar or any other weak acid. The difference between acidic based and electrolysis removal methods is that if you forget something is in the acid it may eventually eat the metal whereas if a non-corrosive electrolyte is used this doesn't happened with electrolysis.

    This is a food grade acid (it's in many soft drinks), and in the 10% concentration used I have never had any burning sensation on my skin, but maybe you should wear gloves.
    Lemons are around 5% CA so your 10% solution it's no different to double strength lemon.

    Note how the acid has pulled off the zinc molecules from the surface of the brass leaving pure copper.
    Strictly speaking the Zn exists on the metal as atoms not molecules.

    Something I discovered the night before whilst cleaning up some router bits: Citric Acid brings Tungsten Carbide up like new - shiny and sparkling. It dissolves and/or soften all the baked on dust, and a quick scrub with a nail brush produces what is apparently a brand new bit! We can deduce that the CA has nil effect on the Carbide because it is shiny straight out of the acid - therefore it will not dull the edges of the bit.
    This is very poor deduction. I would be extremely wary about soaking CT in any acid. The acid may dissolve the binder and weaker the carbide. If you want a way to clean the gummy stuff off CT use caffeine (yes a strong brew of coffee) or just hot water.

    Quote Originally Posted by FenceFurniture View Post
    In using Citric, Acetic and Hydrochloric acids, I've always found the same residue present. I suspect that the black part is converted rust, and the grey underneath is converted steel.
    It is most unlikely that acid can convert rust back into steel - acid treatments usually only dissolve or remove. The black/grey residues are various forms of dissolved iron resulting from leaving the object in the acid for tool long. If it is a weak acid the amount of steel lost will be small but it demonstrates the limitations of the acid method.

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    Cheers, Brett. I reckon just a plastic brush will be fine, I'm not too worried about the blade looking good for now.

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    Bob, I didn't compare the two, I said there were two popular methods.

    If one wanted to use lemons then the time in the solution would presumably be around double, but who wants to cut up and squeeze that many lemons (where a reasonable volume is required. CA (in bulk) is also cheaper than lemons, I should think (unless one has a tree), and can be stored easily for use when lemons are out of season.

    Zn atoms/molecules - relevance? It's no longer there, so what does it matter?

    Electrolysis, whilst having a built in "stop" when there's no more material to work on, is an inherently dangerous practice (particularly for the inexperienced), and sounds like a fair bit of mucking around (from what I've read - I've never tried it). The purpose of this thread was to give a pictorial example of how to go about CA treatment, without commenting on electrolysis. As I said at the outset, both methods have their aficionados.

    "This is very poor deduction." Is that a bit harsh and undiplomatic? I specifically said that we can deduce that it has no effect on the Carbide. No mention of the bonding, so I would say that the deduction is not poor at all. Whether or not it has an effect on the bonding agent is a different matter, and certainly deserves mention, but perhaps in more ambivalent phrasing eh?
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    Quote Originally Posted by BobL View Post
    It is most unlikely that acid can convert rust back into steel - acid treatments usually only dissolve or remove. The black/grey residues are various forms of dissolved iron resulting from leaving the object in the acid for tool long. If it is a weak acid the amount of steel lost will be small but it demonstrates the limitations of the acid method.
    When I said "converted rust" I meant converted into "something else" not steel.
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    Quote Originally Posted by FenceFurniture View Post
    "This is very poor deduction." Is that a bit harsh and undiplomatic? I specifically said that we can deduce that it has no effect on the Carbide. No mention of the bonding, so I would say that the deduction is not poor at all. Whether or not it has an effect on the bonding agent is a different matter, and certainly deserves mention, but perhaps in more ambivalent phrasing eh?
    I'm sorry if you found my response undiplomatic.

    Anyway I was wrong about the CT binder - its not the CT binder that is a problem its the solder used to attach the CT to the body of the cutter. The acid could weaken the solder and could result in a chunk of CT flying off.

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    Quote Originally Posted by FenceFurniture View Post
    When I said "converted rust" I meant converted into "something else" not steel.
    Sorry I misinterpreted what you wrote.

    What colour does the solution turn after the end of process?

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    It starts out quite clear, and goes a pale lime green. There's often a lot of debris at the bottom, as you'd expect.
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    Quote Originally Posted by FenceFurniture View Post
    It starts out quite clear, and goes a pale lime green. There's often a lot of debris at the bottom, as you'd expect.
    The debris is most likely ferrous acetate which is supposed to be insoluble in water.
    This will originate from the converted rust and any dissolve steel.
    The lime green colour means it it is making Ferrous (as as opposed to Ferric) something ions.
    According to Wikipedia ferrous acetate can be used as an iron diet supplement - not that I recommend trying that.

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    I have just used white vinegar 5% acidity by volume and have had good results, perhaps it takes a little longer than the citric but does the job. It also leaves a significant black residue on the item, but with a good wash and a wire brush most of it comes off.
    You can't get something for nothing!

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    Quote Originally Posted by FenceFurniture View Post
    When I said "converted rust" I meant converted into "something else" not steel.

    Phosphoric acid converts red rust into a stable compound ... memory access failure ...

    Don't know about citric acid ... but just found this ...

    How does the acid in lemons (citric acid) help remove rust from clothes? - Yahoo!7 Answers

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    Hi everyone,

    What do you think about the idea of using citric acid or acetic acid to remove lacquer from blades? I tried it and it seemed to do the job quite well, although it made the blade look a lot older very quickly

    Any thoughts on this? I would much prefer to use a non- toxic product like vinegar than acetone for lacquer removal.

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    Quote Originally Posted by Russell Cook View Post
    Hi everyone,

    What do you think about the idea of using citric acid or acetic acid to remove lacquer from blades? I tried it and it seemed to do the job quite well, although it made the blade look a lot older very quickly

    Any thoughts on this? I would much prefer to use a non- toxic product like vinegar than acetone for lacquer removal.
    What sort of blades?

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    The ones I've tried with the vinegar have been manganese steel and what I assume is some kind of cheap carbon steel. I may try HSS in the future, once I've got some high-quality ceramic stones

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