Cyanotype is a low-hazard process: its two iron salts, ferric ammonium citrate and potassium ferricyanide, have low toxicity at the amounts used in the process and are handled with gloves, in a well-ventilated room. Potassium ferricyanide can, however, release cyanide on contact with an acid, or under UV light when in solution: it must therefore never come into contact with an acid.
Cyanotype has a reputation as a gentle process, with no darkroom and no harsh fumes, and it largely deserves it. Even so, it involves two chemical salts, and the question of danger comes up at every workshop, most often prompted by the word ferricyanide, which worries people for the wrong reasons. Here is what this risk really covers, without overstating or downplaying it, along with the few habits that are enough to work with peace of mind.
Safety is not settled once and for all: it comes down to how you measure and handle the chemicals, which ties it directly to the cyanotype recipe and its proportions. If you are coming to the process for the first time, the cyanotype guide puts these habits in the context of the whole practice.
Which chemicals are used in cyanotype
The process relies on two powders that are dissolved in water, ferric ammonium citrate and potassium ferricyanide. They are iron salts that become sensitive to ultraviolet light once mixed, and it is this sensitivity that allows the blue image to form in the sun.
Neither of them is trivial, but neither belongs to the category of highly toxic substances either. As powders and then as solutions, they call for the same care as a household cleaning product: do not breathe in the dust, do not rub your eyes and do not put anything in your mouth.
The one real risk during preparation is the fine powder that can become airborne, so open the bottles without sudden movements and dissolve the salts in water without delay.
The myth of cyanide in cyanotype
The name is frightening, and you sometimes hear that making a cyanotype amounts to handling cyanide. This is a confusion worth clearing up once and for all. Potassium ferricyanide does contain cyanide groups, but they are tightly bound to an iron atom at the heart of the molecule, and this bond is very stable.
In practical terms, 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. The real danger of cyanide, the gas that blocks breathing, does not arise in normal practice: it would take a strong, concentrated acid or intense heat to release a dangerous amount.
The rule that follows is simple:
- never add acid to the sensitiser;
- never let the salts or the baths come into contact with a strong acid;
- never heat a solution;
- do not pour the rinse water away just anywhere.
A very dilute bath of slightly vinegary water, on the other hand, poses no particular danger at the rinsing stage: the chemist Mike Ware, a leading authority on cyanotype, considers a 1% dilute acid bath “not dangerous”.
Prussian blue, a stable pigment
Once the image has been rinsed and has dried, what remains on the paper is no longer the starting salts but Prussian blue, an insoluble pigment that is the very colour of your print. This compound is remarkably stable: it releases neither its iron atoms nor its cyanide groups, which accounts for its durability over time.
It is so stable that it is used in medicine, given in certain cases of heavy metal poisoning, which says a great deal about how inert it is once formed. You can therefore touch and display a finished cyanotype like any other picture. All the care goes into the earlier wet stage, when the salts are still soluble and active.
Safety habits in practice
Protection takes very little and is nothing like laboratory equipment. Nitrile or latex gloves stop the solution from staining and irritating your skin, because beyond the moderate chemical risk, the salts mark your fingers with a stubborn brown stain.
A well-ventilated room, with the window ajar when you open the bottles, takes care of the dust, not out of fear of dangerous fumes, which do not exist here, but so that you do not breathe in the fine powder of the salts.
The rest is common sense: do not drink or eat while handling the chemicals, keep containers aside that will never go back into the kitchen, work on a washable surface and wipe up splashes straight away. These habits quickly become second nature.
- Nitrile or latex gloves
- A well-ventilated room, with the window ajar when you open the bottles
- No acid in the sensitiser, no strong acid in contact with the salts or the baths
- No heated solutions
- No drinking or eating while handling
- Dedicated containers, not used for cooking
- A washable surface, with splashes wiped up straight away
- Reagents stored up high and closed
Putting on gloves and preparing a washable surface before handling the solutions.
Doing cyanotype with children
Cyanotype is a lovely activity to share with children, and the image emerging during the rinse never fails to amaze them, but it should be done under adult supervision. Dividing the roles is the key: the adult keeps the preparation of the solutions and the handling of the bottles, everything that involves the concentrated product.
Children take part in the most rewarding stages: arranging flowers and objects on the sensitised paper, watching the colour change in the sun, then dipping the print in the water. With gloves in their size and the instruction not to touch their face, the risk becomes negligible. Store the reagents up high and closed, as you would a household product.
How to dispose of cyanotype baths
That leaves the rinse water and the dregs of the baths once the session is over. The volumes involved in amateur practice are small and the rinse water is very dilute, but a few precautions are better than a vague approach.
The most straightforward approach is to collect the used baths, leave them to stand so that the Prussian blue settles, then filter out this insoluble sediment before disposing of the clear liquid. Any leftover sensitiser that is still concentrated goes to the household waste recycling centre, along with photographic baths, in the special and hazardous household waste stream.
- Collect the used baths
- Leave them to stand so that the Prussian blue settles
- Filter out this insoluble sediment
- Dispose of the clear liquid, never in a garden, a pond or a watercourse
- Take the leftover concentrated solutions to the household waste recycling centre
Avoid pouring fresh, concentrated solutions straight down the sink, and never empty these baths into a garden, a pond or a watercourse, because dissolved iron salts are not without effect on aquatic life. For rinsing too, it is better to work with controlled volumes of water. Measuring as precisely as the recipe allows reduces, at the source, what you will have to dispose of later.
What to do in case of skin contact
On the skin, rinsing with plenty of water is enough, and any brown stain that remains fades within a few days without consequence. If the solution splashes into your eyes, rinse them for a long time with clean water and seek medical advice if discomfort persists. These incidents remain minor with dilute solutions, but they are a reminder of the value of gloves and a steady hand.
Rather than buying each salt by weight, the Sténoflex cyanotype kit brings together the two bottles, the paper and the pipettes with instructions, which makes a first attempt in good conditions simpler.
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.