Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rust for art-how to & suggestions?

  1. Apr 27, 2007 #1
    Rust for art--how to & suggestions?

    I noticed the topic on making rust from steel wool with vinegar and bleach.
    Can anyone suggest how to form iron rust quickly, but without the chlorine production?
    I am using large steel sheets and trying to produce art-worthy patterns without waiting weeks for the result.
    My thoughts so far:
    1) wet with a strong acid
    2) remove from acid
    3) let rust in humid environment (for wetness and proximity to oxygen)
    4) neutralise with sodium bicarb
    1) immerse in strong acid
    2) oxygenate acid with bubblers (health hazzard would be vaporised acid)
    3) remove and neutralise with sodium bicarb

    Sorry if these suggestions show rusty Chem knowledge, it's been a while!
  2. jcsd
  3. Apr 27, 2007 #2
    Upon further research, Could I ask the following questions (please correct me as I go)
    1) As far as I can tell, HCl would be a good bet for dissolving the Iron (don't know what percent concentration would be ideal of this though): It would seem that the HCl needs time to etch the metal before the Iron is removed from the acid. Does this seem logical? From my friend's tests, a soaking time of 2 hours @ 15% concentration seems necessary
    2) Instead of removing the Iron from the tank, could I simply oxygenate the tank to provide an environment for oxidation & if so, what by-product should I expect apart from Fe2O3?
    3) Would connecting the Iron to an anode & plugging it into DC speed the rusting up? If so, would it also need oxygenation?
    4) For chemical oxidizers, could I mix H2O2 in with the HCl, or would this precipitate a reaction between the compounds? Any dangerous by-products?
    5) For a more hazzardous oxidizer, what about pool chlorine (NaOCl?), and could this be mixed in with the HCl?

    Sorry for the barrage of questions, I'd appreciate any help,
  4. Apr 27, 2007 #3


    User Avatar
    Science Advisor

    Is your goal to make rust, or to rust a piece of metal in a particular pattern?
    Do you want to end up with a pile of Fe2O3, or with a piece of metal with an Iron Oxide coating?

    Hydrochloric acid (HCl (aq)) will readily react with Iron metal to produce Iron (II) Chloride and Hydrogen gas. The Iron Chloride will dissolve in the solution and the Iron metal will be effectively ‘eaten’ away by the acid.
    The Iron Chloride is not rust (although you can make Iron Oxide from it, but it is an unnecessary step in the process).

    Seems to me like you have 3 options to make rust,
    --Allow the process to occur naturally in air (but possibly speed it up with the help of an electrolyte)
    --provide a very oxidizing environment for the Iron with some other oxidizing substance than air
    --Drive the electrochemical process forward yourself with the help of an electric current

    With the help of some electrolyte present, Iron will rust faster. For example, if you leave a piece of steel wool soaking in water (but still exposed to air), it will rust. If you leave the same piece of steel wool soaking in salt water, it will rust faster. Hydrochloric acid is a strong electrolyte, but it will also react with the Iron. Sodium Chloride is also a strong electrolyte, but it will not react with the Iron.
    This process is still somewhat slow, but I am not sure how much Fe2O3 you want, so it might work for you and it is very easy and safe.

    On the other hand, you could provide an even more oxidizing environment for the Iron, more so than in the open air. You could use some oxidizing substance like Sodium Hypochlorite (NaOCl, “bleach”) or Hydrogen Peroxide (H2O2). Both of these substances will oxidize the Iron nicely and much more quickly than it will in the open air. The bleach will probably be easier to use since you can get easily get it in concentrations of about 6% by weight, but then you run into the problem (if you even want to call it that) of the undesirable Chlorine gas formation during the reaction. It is harder, but not impossible, to get concentrations of H2O2 above 3% and H2O2 tends to be much more expensive than bleach, but this does remove the undesired affects of the NaOCl.

    Another way of oxidizing the Iron is to help the process proceed with an electric current.
    Using the Iron metal as the anode of an electrolytic cell (with a wise choice of electrolyte) your production rate will only limited by the current you put through the cell. The higher the current, the faster the Iron will corrode.
  5. Apr 27, 2007 #4
    Thanks for your reply.

    Yes, the idea is to create a good oxide coating, not to oxidise all of the Iron.

    I am interested that the HCl will react with the Iron. Could this be desirable to etch the metal & reduce the overall flaky-ness of the rust? One process I saw for rusting involved using HCL, followed by NaCl (mixed, surprisingly, with Fe2O3) together with H2O2 for oxidization.

    If the HCl forms Fe2Cl with the Iron, could the Fe2Cl be oxidized to form rust (releasing Cl), or would this only occur as a reaction with the remaining iron metal

    Would it be safe to mix NaCl (or HCl) with NaOCl or H2O2 (to provide both an electolyte and an oxidising agent?
  6. Apr 27, 2007 #5


    User Avatar
    Science Advisor

    Hydrochloric acid will react with Iron metal to produce Iron (II) Chloride (aq) and Hydrogen gas. The reaction is as follows,
    2 HCl (aq) + Fe (s) --> H2 (g) + 2 FeCl2 (aq)

    The chemical formula for Iron (II) Chloride is FeCl2 since the Iron ion has a +2 charge on it (as indicated by the Roman numeral in parentheses) and the Chloride ion always has a -1 charge. +2 + 2 * (-1) = 0 net charge.

    A solution of FeCl2 can be used to produce Fe2O3, but it is somewhat complicated. Complicated might not be the right word to use...it is not difficult, but it involves a number of steps which would otherwise be unnecessary had you pursued another way of preparing the Iron Oxide.
    First one would have to oxidize the Iron (II) Chloride to Iron (III) Chloride, when one would need to precipitate out the Fe+3 ion in the form of Iron (III) Hydroxide and filter out the Fe(OH)3. By heating the Fe(OH)3 one can turn it into Fe2O3 and water (and the water will boil off), leaving just Iron (III) Oxide.

    It would be perfectly safe to mix NaCl with HCl, no chemical reaction would occur. Both NaCl and HCl are strong electrolytes. The NaCl will dissolve in solution and break into ions (Na+ and Cl-) along with the H+ ad Cl- already present due to the HCl. So you will end up with a "salty" mixture of acid.
    It would NOT be safe/advisable to mix NaOCl with HCl however since this will produce a lot of very undesirable gasses which are not fun to breathe.
    You can mix NaOCl with H2O2 if you want, but I don’t think you will like the results. Mixing Hydrogen Peroxide with Sodium Hypochlorite will cause the reaction to occur which produces Oxygen gas, water, and Sodium Chloride. It will produce a lot of bubbles and salt water essentially.
    It would probably be best just to stick with one oxidizer; it is generally not the best idea to go around mixing different cleaning chemicals unless you have a pretty good idea what will happen.

    If you just want to create an Iron Oxide coating on the metal, then I think using the bleach method will be best.
    You can get your large sheet of metal you intend to use and "paint" on bleach wherever you want your design to be. Let it sit there for a while as the chemicals do their work, then wash everything off once it has rusted.
    With such small quantities, you shouldn’t need to worry about the fumes coming off the bleach. Just do it outside in the sun.
  7. Apr 27, 2007 #6
    Thanks again!

    Yes, I gained the results you describe.
    NaCl with H2O2 (&Fe) seems to work reasonably (only 3% concentration makes this a bit slow though)
    NaCl with NaOCl (&Fe) works well (faster)

    This leaves a further question: Why the HCl in other's attempts to rust?
    In practice, HCl does not make rust till the iron is removed from the acid. Then it is said by others to rust much better than normal.
    Would I draw the correct conclusion if I said that the HCl must not be acting as an electrolyte for a rust reaction (and that its only benefit would be to cleanse the Iron for normal oxidisation by water vapour & oxygen)?

    Thanks in anticipation
  8. Apr 27, 2007 #7


    User Avatar
    Science Advisor

    My guess is that, maybe,
    -1, the HCl reacts with the Iron and leaves little pits in the surface of the metal. These pits increase the available surface area of the Iron and allow for a quicker oxidization by other materials.
    -2, some of the Iron Chloride produced from the Fe + HCl reaction remains behind on the Iron and acts as an electrolyte (since it is) to help the reaction between the Iron and the Oxygen gas in the air to proceed more easily.

    Also, some Iron is galvanized to protect it against rusting by placing a thin layer of Zinc metal over the Iron. Since Zinc is a more active metal than Iron, it will corrode first, thereby protecting the Iron. In order to oxidize the Iron metal, one must first remove the Zinc. It is very easy to remove Zinc metal with the help of Hydrochloric acid. The Zinc metal with react with the Hydrochloric acid to produce Zinc Chloride in solution and Hydrogen gas. Once the Zinc is gone, the Iron is exposed and is vulnerable to oxidation from the air or other sources.
  9. Apr 27, 2007 #8
    Checking it just now, the iron suspended in the HCl accumulates a grey sediment on its surface after about two hours. This sediment (whatever it is), turns orange almost immediately upon contact with a mixture of NaCl & NaOCl. However, this sediment can then be washed away almost completely.

    Any ideas what the sediment might be? (Iron?)

    Am I correct in thinking that a mixture of NaOCl and NaCl would rust better than NaOCl on its own?

    You've been a super help!
  10. Apr 27, 2007 #9


    User Avatar
    Science Advisor

    I am not sure what that gray stuff could be.
    A solution of Iron (II) Chloride is yellowish in color. If the Fe+2 is further oxidized to Fe+3 (possibly by the NaOCl), you'll have an Iron (III) Chloride solution. A FeCl3 solution is a slightly darker yellow color than FeCl2 (from what I remember, I think) and turns brown in higher concentrations.

    Adding NaCl to NaOCl will certainly not hurt the oxidation process, but I can’t think of any significant benefit of adding it either. Sure, NaCl is a strong electrolyte and will break up into Na+ and Cl- ions in solution and allow for the electrons to pass through the solution more easily. But NaOCl breaks into ions as well. Also, it is the NaOCl which is oxidizing the Iron in that case, not the NaCl. When the bleach oxidized the Iron it turns the NaOCl into NaCl in solution, so whether you add the Sodium Chloride or not it will still be there as a byproduct of the reaction.
  11. Apr 30, 2007 #10
    I wondered, in terms of the surface dynamics, is there any way of rusting the metal in a uniform pattern.

    I find that the rusting process begins in isolated dots, and any attempt to speed up the oxidization only speeds up the development of the dots.

    Is there a way to re-initiate the reaction so that it will cover the whole piece of iron, not in a speckled manner (with clean iron inbetween)

  12. May 1, 2007 #11


    User Avatar
    Science Advisor

    Perhaps making small scratches (for example, by sanding the surface) on the surface where you want the metal to oxidize would help.
    The scratches would increase the available surface area for the oxidization reaction to take place on.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?