Activity 3.5 - Cyanotype

Engaging questions:

  • How does the analog camera work?
  • How are the analog photos created?
  • What does it mean to develop and fix photos?
  • What coloured coordination compounds of iron II and III do you know?

Note: The Activity  can be carried out in one of two ways, depending on the reagents availability.

Reagents:

  • K3[Fe(C2O4)3] CAS:[ 5936-11-8] (version 1), or
  • ammonium iron(III) citrate (preferred – green), CAS: [1185-57-5] (version 2)
  • K3[Fe(CN)6], CAS: 13746-66-2
  • glycerine,
  • citric acid.

Note!  K3[Fe(CN)6] is non-toxic compound, but in contact with strong acids it forms toxic, highly poisonous gases. Citric acid is an irritant compound, during Activity  use a laboratory coat, gloves and protective glasses.

a) Making the photosensitive paper and blueprint photo version 1:

  1. Dissolve 1g of K3[Fe(C2O4)3]  in 25 cm3 of water.
  2. 10 cm3 of this solution pour into the Petri dish and immerse a little blotting-paper disc in it.
  3. Remove the disc with a tweezer and leave it for a while in  an upright position to drain of the solution.
  4. Place paper between paper towel sheets and dry (protect paper from the light).
  5. Dry paper is ready for exposure. The ‘blueprint’ photo can be made e.g. by displaying on the paper the image from the multimedia projector. The illumination time is 20 - 30 minutes, depended on the power of lamp and the type of an image.
  6. After illumination put the disc in the Petri dish with 25 cm3 of 0,03 M K3[Fe(CN)6].
  7. Immerse the blotting paper in the Petri dish with distilled water and dry it again.

 

b) Making the photosensitive paper and blueprint photo version 2:

  1. Weigh out a 90 g of the ammonium iron(III) citrate, transfer it to the flask of 250 cm3 and filling the flask with distilled water up to the mark.
  2. In the second flask of 250 cm3 put 10 g of potassium ferricyanide and fill with the distilled water up to the mark.
  3. Combine the solutions together in a flask or beaker of 1000 cm3 and add about 1 cm3 of glycerol.  Protect the solution from the strong illumination.
  4. Immerse the blotting paper in the prepared solution.
  5. Place paper between paper towel sheets and dry (protect paper from the light).
  6. Dry paper is ready for exposure. The ‘blueprint’ photo can be made e.g. by displaying on the paper the image from the multimedia projector. The illumination time is 20 - 30 minutes, depended on the power of lamp and the type of an image.
  7. After illumination, immerse the blotting paper in 1% solution of citric acid and dry it again.

    Discussion:

    • Thanks to what process the photo was made?
    • Which areas of the image are brighter and which are darker?
    • Blue colour observed on the image is connected with the formation of prussian blue with the formula KFe[Fe(CN)6]. What is an iron degree of oxidation in this compound?
    • What processes need to occur on the blotting paper under the light influence to form this compound?
    • Design an Activity  in which the photo in a form of the positive would be made.