Toning Cyanotypes

Because Prussian blue is nice but can get old

Do Cyanotypes Always Have to Be Blue?

Cyanotypes are often the entry point into alternative photography. Their deep Prussian blue—formed by iron compounds reacting to light—is immediately recognisable.

But that recognisability can also become a limitation.

What’s often overlooked is that cyanotype is not a fixed aesthetic—it’s a starting material. Through bleaching and toning, the image can be transformed into a wide spectrum of colours, using substances as simple as kitchen waste or plant matter.

This is where cyanotype begins to shift from a process you use to a process you work through.

Understanding the transformation: what toning cyanotype actually does

Before going into steps, it’s useful to understand what’s happening.

A finished cyanotype contains Prussian blue (iron(III) ferrocyanide). When you tone a print, you’re not just “adding colour”—you are chemically transforming or partially replacing this compound.

The process usually involves:

1. Bleaching → partially removing or weakening the Prussian blue

2. Toning → introducing tannins or other compounds that react with iron salts, forming new colour complexes

This is why toning is so variable:you are working with residual iron, paper fibres, water chemistry, and organic compounds at the same time.

BLEACHING

Purpose

Bleaching reduces the density of Prussian blue, allowing new compounds to bind more effectively during toning.

Without bleaching, toning still occurs—but tends to be weaker, more subtle, and less predictable.

What actually affects bleaching (more than the “recipe”)

Bleaching is often presented as a formula, but in practice it depends on:

• Water pH

• Water hardness (calcium content)

• Type of bleaching agent

• Print density (how dark your cyanotype is)

• Duration of immersion

Common bleaching agents

• Calcium carbonate (subtle, controllable — often produces more nuanced results)

• Sodium carbonate (soda ash) (stronger, faster)

• Ammonia (effective but can push tones toward brown)

• Detergents (mild alkaline effect)

• Hard tap water (sometimes enough on its own)

I prefer sodium carbonate because it's practical, faster and cheap!

Time and visual cues

Bleaching can take:

• 5 minutes → 45 minutes

Rather than timing alone, look for:→ the print shifting toward a uniform yellow / pale ochre tone

At this point:→ rinse immediately to stop the reaction (super important otherwise it will keep bleaching)

Over-bleaching can remove too much iron, resulting in weak or flat toning later.

TONING

What toning relies on

Most traditional cyanotype toners rely on tannins.

Tannins are plant-based compounds that:

• bind to iron

• form darker or warmer complexes (browns, purples, blacks)

They are found in:

• bark

• leaves

• fruits

• teas and coffee

Common toners

• Black tea → warm browns / sepia

• Coffee → deeper browns, sometimes slightly cooler

• Red wine → muted purples / greys

• Tannin-rich plants (oak, sumac, etc.)

These are popular because they are:

• accessible

• stable

• relatively predictable

Beyond the obvious: unconventional toners

You can use sweet potato peels, onion pit and skin, pomegranade peels, artichokes (the external parts), sage, rosemary, anything that has high concentration of tannins! Variables that change the final colour

Instead of thinking in fixed recipes, it’s more useful to think in variables:

• Bleaching intensity (light vs aggressive)

• Toner concentration

• Time in toner

• Paper / fibre type

• Residual iron in the print

Even changing just one of these can produce a completely different outcome.

I quite like not bleaching my cyanotype print to get a more dense, contrasted and deep in colour print.

From technique to practice

Cyanotype toning is often introduced as a finishing step.

But it can also be approached differently:→ as a way of extending the life of the image-making process

Instead of:

• making a cyanotype → then modifying it

You begin to:

• design the image with its transformation in mind

  
  

This is where it starts to connect to a broader way of working:→ treating processes as evolving, not fixed.

A note on experimentation

Working with:

• kitchen waste

• plant-based materials

• water-dependent variables

means results are inherently inconsistent.

But that inconsistency is not a limitation—it’s what allows the process to remain open, responsive, and specific to your environment.

If you want to push this further

In the Academy, we explore:

• Cyanotype in depth, including modifying density, contrast and tonal range

• Cyanotype on unconventional materials, including glass, and how to tone cyanotype on glass

• How small variable changes affect the outcome

Not as fixed recipes, but as a way of building a deeper understanding of the process over time.

Alternative Processes Academy Explore the Curriculum