Cyanotype chemicals in a rusty old jar

The myth: Don’t use a brush with a metal ferrule! True or not? Malin Fabbri finds out.

It has been said that a brush with a metal ferrule cannot be used for coating cyanotypes, because the metal on the brush may react with the cyanotype chemicals. True or false?

Taking this myth to the extreme, 4 sets of solutions were prepared.

  1. Using glass bowls for mixing the chemicals and a hake brush.
  2. Using glass bowls and a brush with a metal ferrule.
  3. Mixing the chemcials in a rusty jar.
  4. Mixing the chemcials in a rusty jar and leaving the mixed solution in the rust for 24 hours before coating the paper.

Coating the papers, the solution C from the rusty jar was slightly greener than A and B from the glass bowls. Solution D that had been left in the rusty jar for 24 hours was dark green, almost blue when coated onto paper. Clearly a reaction had taken place.

A negative and a Stouffer step wedge were used to make four prints. The prints using solution A (top image) and B from the glass bowl and solution C from the rusty jar were almost identical. But, the print using solution D that had been sitting in the rusty jar for 24 hours was quite different (bottom image). The highlights had oxidized and turned blue.

True or false? The conclusion: False! Though a rusty jar is not recommended when mixing chemicals – a brush with a metal ferrule can be used with no harm. If there is a reaction, it is too small to be noticable.

Beginners guide to cyanotypes
Blueprint to cyanotypes – Exploring a historical alternative photographic process
by Malin Fabbri and Gary Fabbri
A well illustrated step-by-step guide to cyanotypes.
A lot more information on the process, chemicals, coating, exposure, printing, making negatives, washing and troubleshooting is available in this book.
Strongly recommended for beginners


  1. DustyPixie
    Posted May 5, 2011 at 9:41 pm | Permalink

    I used a brush with a metal bit to coat cyanotypes and the odd places where the metal had touched the paper and fabric there where very noticeable dark patches! That was my lesson learnt 🙂

  2. lyn lewis
    Posted July 7, 2011 at 1:36 pm | Permalink

    Guess it might make a difference what metal is on the brushes too?
    Maybe cheaper brushes have thin steel and some others have aluminium? It stands to reason the metal type and content may well cause reactions too?

  3. admin
    Posted July 7, 2011 at 4:37 pm | Permalink

    Well, the point I was trying to make is that a metal brush will not make a difference. See the image “B”, though a rusty jar should be avoided.

  4. Verb
    Posted May 4, 2012 at 7:28 pm | Permalink

    Honestly… I kind of like the results shown with the rusted container, I’m going to have to try this and see it for myself!

  5. admin
    Posted May 5, 2012 at 9:45 am | Permalink

    If you are going to reproduce the result, the jar was VERY rusty. It was a coffee jar in metal found outside in a ditch and has probably been outside for a good 10 years. Please send us the result too, so we can see it!

  6. CC
    Posted September 6, 2014 at 6:25 am | Permalink

    Are there any specific types of metals, that you know of that you would absolutely avoid experimenting with cyanotype chemicals? I was glad to see this article as sooooo many recourses online say not to use metal to mix the stuff but never really say why….this made way more sense as I thought it was a safety purpose, not an exposure/print purpose…… I guess in the long version what I’m asking is if you know of any reason to absolutely avoid any various metal substrate experimentation 🙂

  7. Posted September 6, 2014 at 11:32 am | Permalink

    The jar I used was probably some sort of aluminum. I can’t vouch for the same result on all metals. To be on the safe side, just use a glass jar instead! 🙂

  8. kevs
    Posted March 30, 2015 at 6:42 am | Permalink

    Aluminium doesn’t rust, so Malin’s jar was probably made of (stainless) steel, the main component of which is iron. In contact with oxygen and water, iron oxidises to iron (ii) oxide, aka rust. Although other chemicals or metals may have been used to produce or coat the steel, these would probably have been washed away or otherwide depleted, but could still have been present in the rusty jar s/he used. If anywone wanted to experiment, they could try adding iron (ii) oxide to their cyanotype coatings.

    I’d like to ask Malin whenther the tone in the sky on print D is detail from the negative or a chemical fog. The fog on the step wedge indicates fog, but that could also mean a reduction in contrast allowing the printing of highlight details in the sky.

    Thanks for your time,

  9. Posted April 3, 2015 at 10:56 am | Permalink

    @kevs Thanks for your analysis! There is a slight tone in the sky, but not as heavy as on print D.

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