1. Chemistry of Sun Printing
Cyanotypes

2. Background
Most photography is based on the photochemistry of silver halide salts.
Produces the blacks and grays.

3. Cyanotypes
Involves the photochemical reaction of changing an Iron (III) salt into an iron (II) salt, coupled with a non-photochemical reaction of iron (II) ion with the ferricyanide ion.
Used to be used to create blueprints
Design drawn on translucent paper
Placed over photosensitive paper
Expose to UV light, reacts with paper
Create blueprint.

4. 1st used by Anna Atkins in 1843 to illustrate a book, “Cyanotypes of British and Foreign Flowering Plants and Ferns”

6. The Chemistry The paper is coated with a mixture of 2 substances:
potassium ferricyanide K3[Fe(CN)6]
ferric ammonium citrate (NH4)5[Fe(C6H4O7)2]
When exposed to ultraviolet (UV) light, the following 2 reactions occur:
In (NH4)5[Fe(C6H4O7)2], the Fe3+ ions gains an electron and becomes Fe2+:
(NH4)5[Fe(C6H4O7)2]  Fe2+ (aq) + NH3 (aq) + C6H5O73- (aq)
The Fe2+ reacts with the Fe(CN)63- in K3[Fe(CN)6]:
Fe2+ (aq) + Fe(CN)63- (aq)  Fe3[Fe(CN)6]2 (s)
Prussian Blue