Guides
Part of The cyanotype process: chemistry and safety rules
How to run the cyanotype process safely inside a one-sink flat
A cyanotype process for a one-sink flat: coat, dry, expose and wash with chemical, PPE, ventilation, spill and disposal precautions.
What to take away
- You need shade, not darkness. A closed drawer and a room with the curtains drawn are enough for coating and drying.
- The bathroom is usually the wash station. Clear it completely before you start and clean it after.
- Never spray sensitizer indoors. Coating with a rod or brush keeps the process out of an entirely different hazard class.
- Coated paper stored in the dark keeps for a while. Store it flat, in a light-tight folder, dated.
Splitting the process across a flat
Cyanotype has four stages and they do not need to happen in one room.
Chemicals and handling
Standard cyanotype sensitizer uses ferric ammonium citrate and potassium ferricyanide. Use prepared sensitizer or mix it only as the product label directs, and read the safety data sheet (SDS) for each product. Avoid skin and eye contact or ingestion; potassium ferricyanide can release highly toxic hydrogen cyanide gas if it contacts strong acids, and heat can decompose it. Never mix cyanotype chemicals with acids, cleaners or other chemicals, and do not heat them.
Wear nitrile gloves and splash goggles, cover the work surface, and use tools reserved for cyanotype rather than food preparation. Brush or rod-coat in a ventilated room; do not spray or atomize sensitizer indoors. Keep chemicals and wet work away from children and pets.
Run the cyanotype process
Coat and dry
In subdued light, apply sensitizer to paper with a dedicated brush or coating rod, following the product directions. Dry the paper fully in a dark, ventilated place before exposure, then keep it in a light-tight folder until you are ready to print.
Expose
Place a negative or objects on the dry coated paper and expose it to sunlight or a suitable UV source. Use a test strip and the sensitizer maker's exposure guidance to judge the exposure; conditions vary, so do not rely on a fixed time.
Develop and dry
Develop the exposed print in plain water in a dedicated tray; the blue image develops as the paper washes. Replace the water rather than running the tap continuously, then dry the print flat on a clean board or mesh rack.
Four stages, four places
- Coating: covered table, dim room
- Drying: closed drawer or light-tight box
- Exposure: outdoors, balcony or lamp
- Washing: sink with flat tray
That split is what makes the process practical without a studio. Nothing has to be permanent, and the only fixed requirement is that coated paper never meets daylight before you want it to.
Light control that is actually sufficient
Light rules for coating and drying
- Draw the curtains
- Turn off UV lamps
- Work under warm domestic light
- Exclude light entirely for drying
The National Archives describes the special projects behind the encasement of the founding documents as a long-term environmental control measure. At home, the practical step is simpler: shield coated paper from light and keep it flat and dry in a light-tight folder.
A home version of that reasoning: light and atmosphere degrade your materials, and a closed container controls both.
The ventilation limit worth respecting
Brushing or rod-coating avoids creating the aerosol that spraying produces, but it does not remove the need to prevent skin and eye contact. The federal spray finishing standard is OSHA's 29 CFR 1910.107, which sets controls for covered spray-finishing operations; it is not a general home-ventilation rule. Do not spray or atomize cyanotype sensitizer in a flat, and follow the product SDS for handling and ventilation.
Do not use a cyanotype variant calling for mineral acid or a heated bath in a flat. Strong acids can react with potassium ferricyanide, and heat can decompose it; do not improvise chemical variations. Declining a process is a legitimate technical decision, not a failure of ambition.
The wash station
Set the tray in the bath or a large sink, fill with plain water, and change the water rather than running the tap continuously. Two or three changes clear a print with far less water than a running tap.
Afterward, keep the tray, tongs and jug dedicated to this process, and store them together away from kitchen items. Do not rinse tools in a food-preparation sink or with dishes. Keep unused sensitizer and collected concentrated rinses in a closed, labeled container; do not mix them with other waste or pour them down a drain. Follow the SDS and contact your local household hazardous-waste program for disposal directions. Our kit list for fitting out a print space covers containment and washing items that can make this routine quick.
Spills and first aid
For a spill, keep chemicals out of the sink and do not use another chemical to neutralize them. For a small liquid spill, follow the SDS, wear the stated PPE, and absorb it without spreading it; seal and label cleanup waste and ask your local household hazardous-waste program how to dispose of it. Avoid raising dust from spilled powder, and leave a large spill or one you cannot safely manage to emergency responders.
If chemicals get on skin, remove contaminated clothing and rinse the skin with plenty of water. For eye contact, rinse with clean running water; if inhaled, move to fresh air. If swallowed, rinse the mouth and do not induce vomiting. Contact Poison Control or a medical professional with the product label and SDS; call emergency services for serious symptoms.
Storing coated paper
Coated and fully dried paper keeps for a period in the dark, which lets you coat a batch on one evening and print over several days. Interleave the sheets, keep them flat in a light-tight folder, and write the coating date on the folder rather than the sheets.
These steps cover the process from coating through washing. Our walkthrough of the whole process explains why full drying before exposure matters more than most beginners expect.
