You rinse a cyanotype in clean, cold water, with no added product, changing the bath until the water no longer turns yellow, which takes around five to ten minutes, then you dry it flat away from the sun. Rinsing is the moment the image really appears.
When the paper comes out of the sun, it has a rather dull greenish-yellow tint in which you can barely make out the subject, and it is the water that reveals the blue by carrying away whatever has not reacted. The step looks trivial, you simply pass the sheet under water, but it is what decides whether the print will be deep and stable or pale and faded.
In short, in 5 steps:
- Lay the sheet flat in clean, cold water
- Move the water around the sheet without rubbing
- Change the bath until the water runs clear
- Dry flat, out of direct sunlight
- Judge the blue only once the print is completely dry
This page brings together everything that happens during rinsing: how long it takes, the water turning yellow, the blue darkening as it dries and the role of oxidation. It sticks to rinsing in clean water, the step that follows exposure in the sun, and points to other articles for intensifying, preserving or diagnosing a print. If you are just starting out, bear in mind that this step is part of the process as a whole.
Why rinse a cyanotype after exposure
When it comes out of the sun, the paper holds two things mixed together. Where the UV light struck, the iron has reacted and formed Prussian blue, which is insoluble and firmly anchored in the fibre. Where the paper stayed in the shadow of the negative or the object, the iron salts have not reacted and remain soluble in water, still yellow on the surface.
That is exactly what rinsing is for: dissolving and carrying away these unexposed salts so that only the fixed blue remains. It is the removal of these yellow residues that brings out the contrast. The whites clear, the blues stand out, and an image that was only a greenish-yellow ghost takes on its full depth.
Without rinsing, a cyanotype does not last. The salts left in place would keep reacting to the slightest light, the print would fog and turn brown, and the areas meant to stay white would gradually fill in.
Rinsing is therefore not an optional finishing touch but the step that stops the process and makes the image last. So you rinse the print as soon as it comes out of the sun, without waiting, since those still-soluble salts would otherwise fog the image.
Rinse in clean, cold water
A cyanotype is rinsed in clean water, with no added product. No soap, no fixer, no developer: unlike traditional analogue photography, water alone is enough to carry away the soluble salts, and that is one of the reasons the process is so accessible. A cyanotype kit contains no rinsing product, by the way, only the two bottles of iron salts, the watercolour paper, the pipettes and the instructions.
Cold or lukewarm water is best, never hot, as it dissolves the residues without attacking the layer of blue. Lay the sheet in a basin wide enough to hold it flat, or pass it under a gentle stream of running water, taking care to wet the whole surface in one go to avoid run marks.
Your touch should stay gentle. Prussian blue is firmly fixed, but the surface of the soaked paper remains fragile, and rubbing could tear fibres or mark the image. Instead, move the water around the sheet, change the bath once or twice, and let the water do its work.
Gently move the clean water around without rubbing the surface of the cyanotype.
How long to rinse a cyanotype
Rinsing time is not measured by the clock but by the colour of the water. Keep rinsing as long as the water picks up yellow, and stop when it runs clear. In practice, this takes around five to ten minutes, sometimes a little longer for thick or heavily coated paper that holds more salts.
The most reliable sign is the water turning from yellow to clear. As long as the bath clouds with yellow on contact with the sheet, there are still salts to remove, and once you can change the water without it taking on colour, rinsing is complete.
Changing the water several times rinses better than one long bath in water that becomes saturated with yellow. You often start with a quick first bath that removes most of the residue, then one or two calmer baths that finish the job. Cutting the rinse short is one of the most frequent causes of dirty whites and of prints that later turn brown in the light.
Why the rinse water turns yellow
This yellow water often puzzles people in workshops, and it is nothing to worry about for the image. The yellow you see draining away is precisely the unexposed iron salts, the ferric citrate and ferricyanide that did not react in the sun and that the water dissolves.
Seeing the water change colour is therefore a good sign, proof that the rinse is doing its job. Potassium ferricyanide has low toxicity at the amounts used in the process, but it can release cyanide on contact with an acid, or under UV light when in solution.
One practical point deserves attention: this rinse water contains iron salts and should not be poured away carelessly in large quantities. For occasional home use, dilute it generously, and avoid emptying it into the natural environment.
If the water stays yellow after many minutes without ever clearing, there are two possible explanations. Either the paper was heavily loaded with solution and simply needs more baths, or the exposure was too short and too large a share of the salts did not react. The second case is a matter of diagnosis, covered further on.
The blue that darkens as it dries
Here is the observation that confuses people most: a cyanotype fresh from the rinse often looks pale, grey-blue and a little dull, and you fear the print has failed. It is almost always a false alarm, because the blue formed during exposure has not yet reached its final density and will deepen noticeably as it dries.
This deepening goes hand in hand with oxidation on contact with the air, which speeds up and strengthens the appearance of the full tone, and as it dries the print moves from a faded blue-grey to a deep, rich Prussian blue. So always judge a cyanotype once it is completely dry, never by how it looks coming out of the water.
The print takes anywhere from a few hours to a day to reach its stable colour. Dry it flat, out of direct sunlight so as not to re-expose any remaining residue, in a well-ventilated spot. This patience saves a lot of needless corrections, as many prints judged too light coming out of the water turn out right once dry.
Since this oxidation strengthens the blue, you can also speed it up rather than wait, with a light bath of highly diluted hydrogen peroxide that turns the print to its full blue in a few seconds. The effect is spectacular, but it does not create blue where there is none; it simply reveals all at once the colour that drying would have given.
The limits of rinsing
Sometimes a print remains disappointing once dry, despite correct rinsing. An overall pale, faded blue, greyish whites or an image without contrast cannot be corrected by rinsing for longer, because the problem lies upstream, most often in the exposure, the coating or the paper.
Rinsing reveals the image; it does not create it. If there was not enough light in the sun, the blue will be weak whatever you do in the water, and prolonged rinsing may even carry away part of an already faint blue.
Conversely, a print that is too dark, with the whites gone, comes from overexposure that rinsing cannot rescue. Diagnosing these pale, faded or fogged prints, and the fixes further upstream, are covered in the article on the failed cyanotype, which takes over where rinsing reaches its limits.
After rinsing
Once the sheet has been rinsed and dried, the main work is done: the cyanotype is stable and durable, Prussian blue being one of the most resistant pigments in the process. All that remains is to store it well, away from overly bright light and prolonged humidity, with a few precautions for storage and framing.
Rinsing therefore comes down to a few simple steps: clean, cold water, baths changed until the water runs clear, then drying flat, during which the blue takes on its full depth.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. He has run introductory workshops in alternative photography, from pinhole to cyanotype, from the very beginning.