Cyanotype

What is cyanotype?

Cyanotype is an old photographic technique, created in 1842 by the astronomer and scientist Sir John Herschel. It relies on a photosensitive chemical reaction that generates images in a characteristic blue hue called Prussian blue. Easy to use, this method is ideal for creative and educational projects.

How to prepare a cyanotype solution?

Preparing the photosensitive solution is easy and requires two main chemicals:

• Ferric ammonium citrate (green), a photosensitive compound that reacts to UV light.
• Potassium ferricyanide, which interacts with the citrate to produce Prussian blue.

  To create the solutions:

• Dissolve 25 g of ferric ammonium citrate in 100 ml of water to obtain solution A.
• Dissolve 10 g of potassium ferricyanide in 100 ml of water for solution B.
• Mix the two solutions in equal parts just before use, as the photosensitive mixture degrades quickly in light and over time.

  Immediately apply the mixture to the chosen surface (paper, fabric, wood, etc.) using a brush or sponge. Allow to dry away from light.  

• Once the exposure is complete, gently remove the objects to reveal the pattern.

  Rinsing and drying the solar print:

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  • Immediately immerse the sheet in a basin of clear water to stop the chemical reaction. Gently stir to remove the excess solution.
  • The exposed areas will remain blue, while the protected areas (shadows) will turn white. Continue rinsing until the water is clear (about 2 to 5 minutes).
  • Let the sheet dry completely in open air, flat on an absorbent surface or hung using clothespins.

    And there you have it, your cyanotype is ready to be admired or used as a unique decoration!

• Expose the sheet to sunlight for 5 to 20 minutes. The color of the surface will evolve from light green to gray or dark blue in the areas exposed to light.Good to know: The exposure time for a cyanotype in sunlight varies depending on the season and UV index: Summer (UV index > 6): 1 to 10 minutes - Spring and Fall (UV index between 3 and 6): 5 to 30 minutes - Winter (UV index < 3): from 10 minutes to over an hour.
• Prepare your objects or patterns (opaque objects, leaves, flowers, feathers, or transparencies with printed images). Arrange them on the photosensitive surface.

• Steps to create a cyanotype: