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What went wrong?

My cyanotype highlights are yellow, green or blue-tinged instead of white

Alternative processes

What you're seeing

Whites that should be clean paper look yellowish, greenish, pale blue or lavender.

Check this first

Check this first

Mask a margin of coated paper so it gets no light. After processing, compare it with uncoated paper under bluish light: yellow means the sensitiser has not cleared, blue means fog or bleeding.

Likely causes, most common first

  1. 01

    Sensitiser not fully cleared

    Common
    How to tell
    A yellow tint, easiest to see in the masked margin under bluish light. Sarah Van Keuren: if the water running off the print is yellow, it is not washed enough.
    Test it
    Wash the print a few minutes longer. If the yellow fades, clearing was incomplete.
    The fix
    Wash until no yellow remains in the highlights. Mike Ware gives about 10 to 20 minutes depending on the process.

    Sources Mike Ware, The New Cyanotype Process; Mike Ware, Traditional Cyanotype; AlternativePhotography.com (Sarah van Keuren), A Non-Silver Manual: Cyanotype

  2. 02

    Old mixed sensitiser or stale coated paper

    Common
    How to tell
    Highlights are blue or green all over, and the coated paper already looked greenish before exposure. Mike Ware: if coated paper turns green or blue, the highlights are chemically fogged.
    Test it
    Coat a sheet with freshly mixed sensitiser and process an unexposed piece of it next to an unexposed piece of the old paper.
    The fix
    Mix working sensitiser only when needed and use coated paper within hours. Store it cool, dark and dry.

    Sources Mike Ware, Siderotype Workshop Notes: Simple Cyanotype; Mike Ware, The New Cyanotype Process

  3. 03

    Impurities in the paper

    Occasional
    How to tell
    It happens on one paper only. Mike Ware: a change from lemon-yellow to green on the coated sheet points to impurities or additives hostile to the process.
    Test it
    Coat two papers, leave both in the dark for a few hours, and compare their colour before exposing.
    The fix
    Change paper. Prompt drying can reduce fogging from paper impurities.

    Sources Mike Ware, The New Cyanotype Process; Mike Ware, Siderotype Workshop Notes: Simple Cyanotype

  4. 04

    Highlights blued during acid development

    Occasional
    How to tell
    A pale blue haze in the whites, often near dark areas. Mike Ware notes stained highlights are common from inadequate clearing and bleeding of Prussian blue.
    Test it
    Develop one half of a test print in water and the other in your citric acid bath.
    The fix
    Mike Ware: if highlights are unduly blued, use citric acid weaker than 1%. Blued highlights can be cleared in 1% ammonium oxalate for a few minutes.

    Sources Mike Ware, Siderotype Workshop Notes: Simple Cyanotype; Mike Ware, The New Cyanotype Process

  5. 05

    Delay in humid conditions or incomplete drying

    Occasional
    How to tell
    Lavender tints in the highlights and lower contrast.
    Test it
    Coat two sheets, expose one as soon as it is fully dry and leave the other in a humid room first.
    The fix
    Dry coated paper fully and print it promptly.

    Source AlternativePhotography.com (Sarah van Keuren), A Non-Silver Manual: Cyanotype

Avoiding it next time

  • Mask a margin of coated paper as a clearing check.
  • Mix sensitiser fresh and use coated paper the same day.
  • Keep coated paper cool, dark and dry.

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