The standard cyanotype process uses two chemicals that are relatively low in toxicity. Neither is considered dangerous at the levels used in printmaking, and the process is widely regarded as one of the safest alternative photography techniques. That said, both chemicals are mild irritants, and one of them can become genuinely dangerous under specific conditions.
What’s in Cyanotype Chemistry
A traditional cyanotype sensitizer is a mixture of two compounds: potassium ferricyanide and ferric ammonium citrate. You dissolve each in water separately, then combine them to create a light-sensitive solution that produces the signature deep blue (Prussian blue) image when exposed to ultraviolet light. No other chemicals are strictly needed for the basic process, which is one reason cyanotype is popular with hobbyists, educators, and artists working at home.
Potassium Ferricyanide: Low Risk With One Important Exception
Despite having “cyanide” in its name, potassium ferricyanide is not the same thing as potassium cyanide. The cyanide groups in this compound are tightly bound to an iron atom, which prevents them from acting as a poison in your body the way free cyanide would. Safety data sheets give it a health hazard rating of 1 out of 4 (classified as “slight”), and the lethal dose in lab animals is around 3,000 mg per kilogram of body weight. For context, that puts it in a similar toxicity range to table salt.
At normal working concentrations, potassium ferricyanide can irritate your skin, eyes, and respiratory tract. If you inhale the dry powder while mixing, you may experience coughing or shortness of breath. Swallowing a large amount could cause nausea, vomiting, diarrhea, and cramping. These are nuisance-level effects, not emergencies.
The real hazard is chemical, not biological. When potassium ferricyanide is heated to high temperatures or comes into contact with strong acids, it releases hydrogen cyanide gas, which is extremely toxic. This means you should never heat your cyanotype solution over a flame, mix it with acidic chemicals like vinegar or muriatic acid, or dispose of it in a way that could expose it to acid fumes. Under normal room-temperature printmaking conditions, this reaction does not occur.
Ferric Ammonium Citrate: A Mild Irritant
The second chemical, ferric ammonium citrate, is even less hazardous. It’s an iron-based compound sometimes used as an iron supplement in food fortification. Direct contact can irritate your skin and eyes, and prolonged eye exposure may cause a brownish discoloration. The New Jersey Department of Health recommends wearing nitrile or natural rubber gloves when handling it and washing your hands before eating, drinking, or touching your face.
The Dichromate Problem
Some cyanotype practitioners have historically used potassium dichromate as a fixative or contrast-boosting additive. This is a completely different chemical, and it is genuinely dangerous. Potassium dichromate contains hexavalent chromium, a known carcinogen and potent skin sensitizer.
A NIOSH investigation documented the case of an artist who used a dichromate-based cyanotype process to print images onto quilt fabric. She developed facial and finger swelling, mucous membrane irritation, headaches, and nausea. Even after she stopped making new prints, her symptoms returned whenever she handled or sewed the treated cloth. Testing found hexavalent chromium contamination on her work surfaces. Investigators recommended she stop using dichromate entirely, decontaminate her workspace with soap and water, and thoroughly wash all treated fabrics in hot water.
If you’re following a traditional two-chemical cyanotype recipe (ferric ammonium citrate and potassium ferricyanide only), this risk does not apply to you. But if a recipe or kit calls for any chromium-based additive, treat it as a significant health concern.
Safe Handling Practices
For the standard cyanotype process, basic precautions are enough:
- Wear nitrile gloves when mixing and coating. Both chemicals stain skin and can cause mild irritation with repeated exposure.
- Mix powders carefully. The biggest inhalation risk comes from scooping dry potassium ferricyanide. Work in a ventilated area and avoid creating dust clouds. A simple dust mask helps if you mix chemicals frequently.
- Keep acids away. Never combine your cyanotype solution with vinegar, citric acid crystals, or any strong acid. Some toning recipes call for acidic baths after printing, so keep these steps physically separate and ensure good ventilation.
- Don’t heat the solution. There is no reason to warm cyanotype chemicals. Drying coated paper or fabric at room temperature or with a cool fan is sufficient.
- Wash your hands before eating, drinking, or touching your face.
Are Finished Cyanotype Prints Safe to Handle?
A properly processed cyanotype print that has been rinsed thoroughly in water poses minimal risk. The final image is Prussian blue, an insoluble pigment that sits in the fibers of the paper or fabric. It doesn’t leach out easily, and it’s the same pigment historically used in laundry bluing and some cosmetics.
The NIOSH case where an artist reacted to finished fabric involved potassium dichromate residue, not the standard cyanotype chemicals. If you’re printing on fabric you plan to wear or use in a quilt, stick to the basic two-chemical formula, rinse the fabric thoroughly in running water after development, and skip any chromium-based additives. Fabric treated this way and washed well should not cause skin reactions.
Is Cyanotype Safe for Kids?
Cyanotype is one of the more child-friendly photographic processes, and pre-coated sun print paper (sold in many toy and science kits) removes the chemical mixing step entirely. If children are working with liquid sensitizer, an adult should handle the mixing of dry powders, and kids should wear gloves during coating. The main practical concern is staining: the solution will turn fingers, clothes, and work surfaces a stubborn yellow-brown that’s difficult to remove.