How to write a message using light in 1 minute
How does cyanotype work
We’re used to drawing with pens and pencils – but how about using chemistry and light? In this experiment, we’ll show you how to write using these two rather unexpected elements.
Wear protective gloves, glasses, and a mask. Work in a well-ventilated area.
Reagents and equipment
- 10 mL 1.5 mol/L citric acid solution;
- 10 mL 1 mol/L ammonium iron(III) sulfate;
- 10 mL 1 mol/L ammonium carbonate solution;
- 10 mL 1 mol/L red prussiate of potash (potassium hexacyanoferrate(III)) solution;
- 2 glass bowls;
- 1 flashlight;
- cotton absorbents;
- 1 sheet of watercolor paper.
Prepare your light-sensitive solution in the first bowl: mix the solutions of citric acid, ammonium iron(III) sulfate, ammonium carbonate, and red prussiate of potash (potassium hexacyanoferrate(III)). Mix thoroughly. Make sure to work in dim lighting to keep the solution from reacting prematurely. Next, take a sheet of watercolor paper and apply an even coating of the solution using a cotton absorbent. Use your flashlight to write a message. Watch the solution transform! Fill your second glass bowl with water and rinse the treated paper thoroughly to remove any extra solution.
Ammonium iron(III) sulfate and citric acid react to form light-sensitive ammonium iron(III) citrate. When exposed to light, citrate ions reduce iron(III) ions to iron(II) ions, which react with potassium hexacyanoferrate(III) to form a striking blue pigment known as Prussian blue. This reaction is the foundation for a printing method known as cyanotype, which was once used to print plans and various documents. Such prints were therefore known as blueprints.