Sun Print Cyanotype Kids Can Make Without a Camera

A photograph without a camera, without a lens and without a darkroom takes about four minutes. Lay a fern leaf and a house key on a sheet of light-sensitive paper, carry it outside, come back, rinse it under the tap, and you have a sharp white silhouette on deep blue paper that will still be there in fifty years. This is a sun print cyanotype kids can run almost unaided, and it is a real photographic process, invented in 1842 and still used by artists and architects. One rule comes before everything: you expose the paper in sunlight, and you never look at the sun while you do it. Put the paper down, walk away, and let the light work.

Key Takeaways

• You place objects on coated paper, expose it to sunlight for one to five minutes, and rinse it in cool water to fix the image.
• The chemistry is iron, not silver. Ultraviolet light reduces iron(III) to iron(II), which reacts to form the pigment Prussian blue.
• Assemble the print indoors in dim light. Pre-exposure while you arrange leaves on a sunny table is the single most common failure.
• Never look at the sun while exposing, and never use a magnifier to speed it up. Place, leave, return.
• Best for ages 6 to 12 with pre-coated paper. Mixing your own solution is an adults-only job for reasons in the safety table.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Pre-coated cyanotype or sun-print paper	4–8 sheets	Art shops, science suppliers, online	There is no household substitute that gives a permanent image. Coloured construction paper fades in sunlight, which is a different process and takes days
Flat objects to print	5–10	Leaves, ferns, feathers, keys, lace, paper cut-outs, washers	Anything opaque and flat. Thick objects give fuzzy edges
Sheet of glass or clear acrylic	1, slightly larger than the paper	A clip frame, a picture-frame pane	A clear plastic folder, taped flat. Adults handle glass and tape the edges
Stiff board	1	Cardboard, a clipboard	Anything rigid to carry the sandwich outside flat
Shallow tray of cool water	1	A washing-up bowl	The kitchen sink
Kitchen timer	1	A phone	Exposure time is the main variable you will be testing
Dark envelope or drawer	1	n/a	To store unexposed paper. Light-tight storage matters
Paper towels and a flat drying space	n/a	n/a	n/a

Time: prep 10 min, exposure 1–20 min depending on sun, rinse and dry 20 min Cost: a pack of cyanotype paper is the main expense, about the price of two coffees for a dozen sheets Mess level: low, though the rinse water turns pale yellow-green

Do the Experiment: A Sun Print Cyanotype Kids Can Make

Step 1 - Find your light before you open the packet

Step outside and look at your shadow, with your back to the sun. A hard-edged shadow means strong direct sun and exposures near one to two minutes. A soft shadow means overcast, and exposures of five to twenty minutes. Decide this first, because once the paper is out you are on the clock.

Step 2 - Set up indoors, in dim light

Close the curtains or work in a hallway away from windows. Take out one sheet, coated side up, lay your objects on it, and press the whole thing under the glass so everything is in firm contact. Any gap between object and paper lets light creep sideways and softens the edge.

Step 3 - Ask for the prediction

Ask: “The paper is one colour now. After the sun and the water, will the parts under the leaf be darker or lighter than the rest?” Most children say darker, reasoning that the leaf protects the colour. Write it down.

Step 4 - Carry it out, set it down, and walk away

Take the sandwich outside on its board, lay it flat in direct sun, start the timer, and step back. Do not look up at the sun. Do not hold a magnifier over it. Give it 1 to 2 minutes in strong sun, 5 to 20 in overcast.

What you should see: The exposed areas of the coating change colour visibly during the exposure, typically from yellow-green toward a dull bronze or grey-blue, while the covered areas stay as they were. This is not the final image, and it will look disappointing at this stage. Trust the rinse.

Step 5 - Rinse in cool water for a full minute

Bring it inside, lift off the objects, and slide the paper into the tray of cool water. Agitate gently for at least a minute, longer if the water is cloudy, then change the water and rinse again.

What you should see: The blue deepens dramatically in the water while the covered areas wash out to the white of the paper. The reversal relative to the dry appearance surprises nearly everyone, including the adults, and it is the moment the activity turns from craft into chemistry.

Step 6 - Dry it flat and check the next day

Lay it on a paper towel, out of sunlight, and leave it overnight.

What you should see: The blue continues to intensify over several hours as the Prussian blue fully oxidises. A print that looked weak when wet is often rich by morning. If it instead fades or yellows, it was not rinsed long enough.

Step 7 - Run an exposure series

Take one sheet, lay a single leaf across it, and cover the sheet with card. Slide the card back to uncover a strip every so often: 15 seconds, 30 seconds, 1, 2, 4 and 8 minutes of total exposure. Rinse normally.

What you should see: A step wedge. The shortest strip is pale and the longest is dark, and somewhere in the middle is the exposure that gives the best contrast between leaf and background. That strip is your correct exposure for today’s light, which is exactly how photographers worked before meters.

What’s Actually Going On

This is photochemistry, and the active element is iron. Cyanotype paper carries two salts: ammonium iron(III) citrate and potassium ferricyanide. In the dark, nothing much happens between them.

Ultraviolet and short-wavelength visible light, roughly 300 to 400 nm, are absorbed by the iron(III) citrate complex, and the energy drives an internal electron transfer: the citrate is oxidised and the iron is reduced from iron(III) to iron(II). That is the light-sensitive step, and it is the only step the sun does. The iron(II) then reacts with the ferricyanide ion to form an intensely coloured, insoluble compound, ferric ferrocyanide, better known as Prussian blue, with the approximate formula Fe₄[Fe(CN)₆]₃. Because it is insoluble, it stays in the paper fibres when you rinse. The unreacted salts in the covered areas are water-soluble, so they wash out and leave bare white paper. The rinse is not just cleaning; it is the development and the fixing step in one.

Sir John Herschel described this and several related processes in a paper in the Philosophical Transactions of the Royal Society in 1842, under the characteristically Victorian title “On the action of the rays of the solar spectrum on vegetable colours, and on some new photographic processes.” Glen Lawrence and Stuart Fishelson published a classroom treatment of the chemistry in the Journal of Chemical Education in 1999 if you want the procedure written up for a lab.

Three practical consequences fall straight out of the mechanism.

First, the process responds to the part of the spectrum your eyes cannot see. That means the paper is far more sensitive to a hazy blue sky than its brightness suggests, and it means the print works through a window, more slowly, because ordinary glass transmits a good share of UVA while blocking most UVB. If you have run the UV bead and sunscreen experiment, this is the same invisible light doing a different job, and you can even smear sunscreen on the covering glass and print its shadow.

Second, there is no amplification. Unlike silver photography, where a few photons create a latent image that chemical development multiplies enormously, each cyanotype molecule has to absorb its own photon. That is why exposures are minutes rather than fractions of a second, and why a camera cyanotype needs bright sun and patience.

Third, the image is permanent in a way most craft activities are not. Prussian blue is stable and lightfast, which is why nineteenth-century blueprints survive and why Anna Atkins’s cyanotype botanical plates from the 1840s are still legible. A well-rinsed print will outlast the child who made it. Prints that fade have almost always been under-rinsed, leaving soluble iron salts in the paper.

How to Explain It to Your Kid

Ages 5–8: The sun draws around whatever you put down

Say the paper is waiting for sunlight, and anywhere the sun touches it will turn blue, so anything they lay down leaves its own shape behind. Let them choose the objects, which is the real pleasure, and let them put their hand on a sheet for two minutes and see their own handprint. Keep the explanation to sun plus paper equals blue, and object equals white.

Ages 9–12: Invisible light and a colour change

Introduce ultraviolet and the key idea that the chemical change is caused by light the eye cannot detect. Then do the exposure series in Step 7, because it makes the relationship between time and result quantitative. Ask them why the print looks wrong before the rinse, and let them work out that the water is doing two jobs: finishing the reaction and washing away everything that did not react.

Ages 13+: Redox, and why there is no amplification

Give them the full redox picture: light-driven reduction of iron(III) to iron(II), followed by the formation of insoluble Prussian blue. Then ask the sharp question: why does a photographic film need only a thousandth of a second in the same sunlight that a cyanotype needs two minutes for? The answer, chemical development amplifying a latent image by a factor of millions, is one of the genuinely clever ideas in the history of chemistry.

The question to ask: “If we printed the same leaf at eight in the morning and again at noon on the same day, would the exposure time need to be longer, shorter or the same? Say which and why, before we test it.”

Why Teaching This Early Pays Off

Most chemistry a child meets at home is acid and base, or dissolving and precipitating. Photochemistry is a different category: light as a reagent, driving a reaction that will not happen in the dark. That reframing matters later for photosynthesis, for vitamin D synthesis in skin and for every solar cell, and it is hard to teach abstractly.

It also demonstrates permanence, which is rarer in kitchen science than you would think. A cyanotype is a physical object the child made with sunlight that will still exist in twenty years, and that does quiet work in making the activity feel serious rather than disposable.

The honest limit is the usual one. One print teaches a procedure, not a discipline. What transfers is the habit the exposure series builds: change one variable, hold everything else constant, read the result off a strip of paper. The National Research Council’s framework puts planning and carrying out investigations among its core practices, and a step wedge is the simplest honest version a family can make.

Before You Start: What Parents Should Know

Best age	6 to 12 with pre-coated paper. Under 6 with an adult placing the objects
Supervision	Close for the first print. Adult handles glass and any chemicals
Real hazards	Looking at the sun. You are deliberately working in direct sunlight, and children will want to check “how sunny it is”. Solar retinopathy can be permanent and is often painless as it occurs; NASA states that no sunglasses, stacked sunglasses, exposed film, smoked glass or improvised filter makes direct solar viewing safe. Set the print down and turn away. Never use a lens or magnifier to speed exposure: it is both a fire risk and an eye risk. Glass panes chip; tape the edges. The rinse water is dilute but should not be drunk, and hands should be washed afterwards
Don’t	Don’t mix your own cyanotype solution with children present. Potassium ferricyanide is listed on PubChem with hazard statements including harmful if swallowed, causes skin irritation, causes serious eye irritation, and toxic to aquatic life with long-lasting effects. It must never be brought into contact with acid. Pre-coated paper avoids all of this, and that is why this guide recommends it

When It Doesn’t Work

• The whole sheet turns blue, including under the objects. You assembled it in daylight. The paper starts reacting the moment it sees a bright window. Work in a dim hallway, and keep spare sheets in a closed drawer.
• The image is pale and washes away. Under-exposed, or the paper is old. Run the exposure series in Step 7 to find today’s correct time. Paper stored warm or in a bright room loses sensitivity over months.
• The whole print is dark with no contrast. Over-exposed. In strong summer sun, one minute can be plenty. Halve the time.
• The edges of the leaf are fuzzy. The object was not in firm contact with the paper. Press everything under glass, and prefer flat, pressed leaves to curled fresh ones.
• It looked good when wet and faded within a week. Under-rinsed. Soluble salts left in the paper keep reacting. Rinse for a full minute, change the water, and rinse again until the water runs clear.

Take It Further

• Print through different filters. Make four prints under the same sun, each covered with a different barrier: clear glass, glass smeared with sunscreen, a sheet of clear plastic, and nothing. Time them to the same exposure and compare. You are measuring UV transmission with photographic paper, which is a genuine instrument.
• Make a photogram of something translucent. A slice of lemon, a feather, a piece of lace or a negative printed on acetate from an inkjet printer produces continuous tones rather than a flat silhouette, because the light is partly transmitted. This is where a sun print starts to behave like real photography.
• Combine it with a lens-free camera. Load a sheet into the back of the device from our guide to building a pinhole camera, in a dark room, and expose for several minutes pointed at a sunlit scene. Expect a faint, soft, inverted image and a high chance of failure on the first attempt, which is exactly how early photography went. The separation of pigments in the rinse water also rewards the attention you gave paper chromatography.

What to Watch For Over the Next 3 Months

• Week 4: They start noticing that sunlight changes things over time: a faded book spine on a windowsill, a sun-bleached plastic toy left in the garden.
• Month 2: The phrase “ultraviolet” gets used correctly about something that is not sunburn. Watch for it in connection with the print taking longer in the shade.
• Month 3: If they ask how a film camera managed to take a photograph in a fraction of a second when this takes minutes, they have found the question that explains the entire history of photographic chemistry.

Frequently Asked Questions

Why does the print look wrong before I rinse it?

Because the visible colour change during exposure is only the first step. The rinse completes the formation of insoluble Prussian blue in the exposed areas and washes the unreacted, water-soluble salts out of the covered areas. The image effectively appears in the water.

How long should I expose it?

One to two minutes in strong direct sun, five to twenty in overcast conditions. Rather than guessing, make an exposure series on a single sheet with strips at 15 seconds, 30 seconds, 1, 2, 4 and 8 minutes, and read off the best result for your light.

Can I use coloured paper instead of buying cyanotype paper?

It is a different and much weaker process. Construction paper fades where sunlight bleaches its dyes, which takes days in a window and gives a low-contrast, impermanent result. Cyanotype chemistry gives a sharp, lightfast image in minutes.

Does it work on a cloudy day or behind a window?

Yes to both, more slowly. The process responds to ultraviolet, and plenty of UVA reaches you through cloud and ordinary glass.

Is the chemistry safe for a child to handle?

Pre-coated paper, handled dry and then rinsed, is suitable with normal supervision and handwashing afterwards. Mixing your own solution is not: potassium ferricyanide is harmful if swallowed, irritates skin and eyes, is toxic to aquatic life, and must never meet acid.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Herschel, J. F. W. (1842). “On the action of the rays of the solar spectrum on vegetable colours, and on some new photographic processes.” Philosophical Transactions of the Royal Society of London, 132, 181–214. https://doi.org/10.1098/rstl.1842.0013
2. Lawrence, G. D., & Fishelson, S. (1999). “Blueprint Photography by the Cyanotype Process.” Journal of Chemical Education, 76(9), 1216A. https://doi.org/10.1021/ed076p1216a
3. National Center for Biotechnology Information. “Potassium ferricyanide, CID 26250.” PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/26250
4. NASA Science. “Ultraviolet Waves.” Tour of the Electromagnetic Spectrum. https://science.nasa.gov/ems/10_ultravioletwaves/
5. NASA Science. “Eclipse Viewing Safety.” https://science.nasa.gov/eclipses/safety/
6. American Academy of Ophthalmology. “Solar Eclipse Eye Safety.” https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety
7. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. https://doi.org/10.17226/13165