Question

In this part of today's experiment you will produce cyanotypes using watercolor paper. Directions 1. Each student should obtain a piece of 4” x 5” watercolor paper. Work with ONE partner. 2. Each pair should prepare the following solution in a 250 mL beaker. 1.2g ferric ammonium citrate 0.6g potassium ferricyanide 20 mL of water 3. Stir until dissolved and describe the color of the mixed solution. ______________________ 4. Place the paper in one of the plastic trays under the hood. Using a flat foam brush, coat one side completely with the solution. Wipe first in one direction and then a second time at a right angle to the first direction. 5. CAREFULLY dry the paper using a hot air gun, or place in the oven in the Prep room. 6. When dry, print the dry paper by clipping a large negative image on top of the paper and exposing it to sunlight (outside, if it’s sunny) or a UV light source (inside). 7. When the exposed regions of the paper are changed in color to a deep blue-green, unclip and remove the negative. 8. Wash the paper with a gentle stream of tap water to remove the soluble unreacted light sensitive chemicals. 9. Dry the blueprints with a hot air gun, or in the oven in the Prep room.

Discussion Questions

1. What develops the image?

2. What works as the fixer for the image?

3. Write balanced chemical equations for the reactions observed.

Answer 1

1. When the paper is treated with a solution of potassium ferricyanide and ferric ammonium citrate it produces a photosensitive compound, iron (III) hexacyanoferrate (III). When this paper is exposed to the light the light reduces the ferric ion (+3) to ferrous ion (+2).

2. This ferrous ion then react with the potassium ferricyanide to produce iron (III) hexacyanoferrate (II), which is an insoluble, deep blue coloured compound called Prussian blue which forms the blue part of the final blueprint.

3. Reactions

The citrate and oxalate are the anions generated by the loss of two acidic protons from citric and oxalic acid. Interaction of light with these forms to their oxidation and releases carbon dioxide and an electron which reduces iron (III) to iron (II). These Fe(II) combines with CN- present in the solution to form the complex gives prussion ble Fe(III)4[Fe(CN)6]3 adhering to the paper.