Create an image using light!

25 minutes
Experiment's video preview



  • Conduct the experiment on the plastic tray.
  • Put on protective gloves and eyewear.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

I stained my table with the blue dye. How can I wash it off?

This dye can easily be removed using a solution of NaHCO3. Dissolve 1 teaspoon of baking soda (sodium bicarbonate) in a glass of water, moisten a cloth with the resulting solution, and wipe the stains off the affected surface.

The mixture that I obtained isn’t yellow. What should I do?

If, at this stage of the experiment, you notice blue stripes on a yellow background, take a new absorbent and keep applying the mixture to the paper.

However, if the whole mixture has turned blue, this likely means that you’ve overexposed it to light. But don’t worry! Just discard this plastic cup and start over. When repeating the experiment, keep in mind that the experiment must be performed in very dim lighting.

And if the mixture turned greenish? It’ll still work, but the drawing won’t be as contrasted.

Which lamps will work for this experiment?

For this experiment, you can use:
- 75 W incandescent light (including halogen);
- 11 W LED or fluorescent light.
Your lamp must be positioned approximately 12 in. (30 cm) from the paper. Leave the paper exposed to light for 10-15 min. If your light source is more powerful than the references listed above, keep it farther away from the paper. A 100 W light source should be positioned approximately 16 in. (40 cm) away.

It’s been 10 minutes, but the drawing is still very pale. What should I do?

If you haven’t washed your drawing yet, leave the paper under the light for 5-10 more minutes.

Step-by-step instructions

As we will be dealing with light-sensitive compounds, we need to avoid bright light, such as direct sunlight or strong lamps.


Prepare the plexiglas plate.


First, prepare light-sensitive ammonium iron(III) citrate by causing an ion exchange reaction between ammonium iron(III) sulfate and citric acid.


Mix ammonium iron(III) citrate with potassium hexacyanoferrate(III). This mixture is the key to making our print visible.


Now apply the photosensitive mixture to a paper.


Use the transparent negative image to protect some parts of the paper from light.


Under the impact of light, iron ions in ammonium iron(III) citrate are reduced to iron(II). Which in turn react with potassium hexacyanoferrate(III) to produce a stable blue compound–Prussian blue.


After removing the excess of the photosensitive mixture, we are left with a nice blue and white image.



Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

When light hits an iron ion Fe3+ from ammonium iron(III) citrate, it initiates a reaction in which Fe3+ gains an electron , turning (or, as chemists say, reducing) into Fe2+ . But the product of this reaction is not yet visible, and that’s where potassium hexacyanoferrate(III) comes into play. It does not stick to Fe3+ , but once it meets Fe2+ , it forms an insoluble intensely-colored compound called Prussian blue. This is what we see when we look at a cyanotype image.

Nowadays, this process is used mostly by hobbyists to print photos or even decorate clothes. But in the second half of the nineteenth and early twentieth centuries, it was used much more widely for copying technical drawings. That’s why architectural plans and technical drawings are still often called blueprints.

The cyanotype process is not the only way to obtain Prussian blue. In fact, this stunningly blue compound was known as one of the best blue pigments well before cyanotype was invented. Many works of art owe it their striking shades of blue—Hokusai’s “Great Wave”, which we have just made a print of, for one.

That's interesting!

Cyanotype and blueprints

Cyanotyping was historically used in some industrial fields to create what are known as blueprints. The term ‘blueprint’ usually refers to engineering-specific technical drawings. The blueprint was mostly used in the 19th and 20th centuries to copy technical drawings of buildings and ships. However, with the advent of industrial printers, this method gradually lost popularity, and now is most often used by hobbyists.

The method’s “blue” name is, indeed, because the result is blue. A bit later, another method was developed, which differs mostly in the resulting color - the images range from pinkish to pure white. Such a picture is known as a whiteprint. The reagents that contribute to this process differ vastly from those used to create a blueprint, the key substances being organic compounds containing diazo compounds.