For conservators working with iron, rust is always a consideration.  In museum collections or in our homes, we easily encounter rusty fences, grates, car parts, artwork and collectibles.  Iron oxide (commonly called rust) results from the natural oxidation of iron by oxygen.  Some metals, like bronze, can form a protective layer of corrosion products called a “patina.”  However, iron corrosion will continue to negatively affect an object until treated.  Rust is destructive, not protective.

To combat this destruction, conservators utilize a few different methods.  For artifacts not containing heavy chlorine-induced corrosion (objects not heavy in salts or near salt water), rust conversion is a reliable avenue for protection.  Rust converters, most often containing tannic acid or phosphoric acid, react with the iron oxides to form a stable layer on the exterior of the treated object.  There are many commercially available rust converters that are accessible to both the professional conservator and concerned homeowner.   However all rust converters do not function equally well, especially over a long period of time.

With these concerns in mind, NCPTT’s Materials Research Program undertakes a new study this summer centering on the effective treatment of rust.  In this comparative study, we will investigate which product most completely converts rust and which product performs best over a period of extended exposure.  We want to determine which rust converters are both effective and long-lasting.

Photographing rust study samples before treatment begins

The experiment follows this basic structure: (1) Document physical condition, (2) Analyze chemical condition, (3) Artificially weather.

To document the physical condition of the samples, we photograph our rusted sheet metal samples at various points in the experiment.  Additionally, a laser profilometer records a three dimensional map of the sample surface and any changes in that surface during the experiment.

We use a number of analytical techniques in our analysis of the chemical condition.   First, a Fourier-Transform Infrared Spectrometer (FT-IR) helps us characterize the chemical structure of the primary compounds in the surface of the sample.  After treatment and as the weathering progresses, the FT-IR allows our research team to chart the chemical changes occurring in the surface of the sample.  We also quantitatively measure the color, gloss, and coating thickness using a colorimeter, a glossmeter and a magnetic induction instrument (respectively).

Analyzing a sample using a Fourier Transform Infrared Spectrometer

Finally, we simulate natural exposure of our samples through the UV exposure and condensation cycles of an artificial weathering instrument (called a QUV weatherometer).  The artificial weathering admittedly differs in certain ways from natural weathering.  However, this process provides a controlled environment in which to begin studying the long-term efficacy of the rust converters.  The samples are periodically removed during the weathering process so that the condition can be documented and chemical analyses can be performed.

When the study concludes, we hope to have the scientific data to compare the performance of commercially available rust converters based on their efficacy and durability.  This information can then be used in the effective treatment of rusty objects—whether that item will be displayed in a museum or on a back porch.

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14 Responses to Materials Research Program Begins Rust Converter Study

  1. John Leeke says:

    I would like to implement a side-by-side comparative field test of rust treatments that is coordinated with your testing. I’d like to run this field test concurrent with your testing so the results can be analyzed along with the release of your results, at the same time.

    Could you please describe the specifics and details of which products and materials you will be testing, methods of surface preparation, method of applications, etc.

    Thanks for all your good work there at NCPTT.

    John Leeke
    American Preservationeer

  2. John Leeke says:

    I’m still hoping to here from the “rusticators” so I can coordinate a field test with your study.

    American Preservationeer

  3. James Milnar says:

    Hi Folks, caught your work while web researching corrosion coatings/prep-
    paint per autobody resroration. As a Detroiter, we here tend to be
    very big on restoring and parading our sweetly fixed old cars.
    You all may be familiar with Michigans- Woodward Ave Cruise, as paritcipated
    by so many and including collector car guy/comedian Jay Leno.
    Presently I too, caught up in a multi-rustspot repair, a 2000 Dakota.
    Trying hard to come up with a best practice method- rust prep, short of
    sandblasting,with some tite rustleft, that that follows with 2k epoxy prime
    and topcoat or other… that will last up here, wet and salty winters.

    So I am going to be very interested in your findings re; performance of
    the conversion coatings. Did catch a TSB(bulletin) from Ford regarding
    some premature rust on doors of a production vehicle and therein
    requested use of SEM’s- RustSeal39308 conversion coating(milky acrylic
    emulsion/phosphoric based) followed with spec primer and topcoat for repair.

    Also, you may already be aware, but if not, Your Benchmark performance
    comparison may be- Amercoat 236 over Devoe Pre-Prime 167(super thin and
    saturating epoxy), currently used on numerous ship hulls and deck
    above and below waterline. These are all epoxy and spec where Rust will
    Not be Completely Removed per SSPC-SP2,or3. So be sure to include a sample
    and scratch that one in your salt spray box and see how the rest compare.

    Good Luck, sure appreciate your hard work and may you find a great product
    discovery that costs less,stinks less,works great under standard and’green’
    paint systems…..and let the world know
    thanks, James

  4. […] Materials Research Program Begins Rust Converter Study […]

  5. John Leeke says:

    Are there any results from the rust study?


  6. konrad Streuli says:

    have you reached any conclusions regarding your 2010 rust converter study?

    are they available?

    many thanks

    konrad streuli

    • The Rust Converter Study is being written up for publication by Jason church. Additionally, he has expanded the study and is continuing his research efforts. check back on or website soon or contact Jason directly.

      • Benjamin Cook says:

        I would like to know the pH range at which ferric tannate can form, without using a phosphate. Also, quite interested in getting the survey when completed.

  7. Farokh Mehr says:

    Is the study out?

  8. ask says:

    It’s difficult to find well-informed people in this particular subject, but you sound like you know what you’re talking about!


  9. Bastawy says:

    I’d like to know how we can select the right rust converter for the risers and piles of the platforms and what is the test and performance procedure for any of this product

    Thank you

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