1. The Chemistry of Photography
Peter Jantz
Chemistry 496
February 27, 2004

2. Black and White Film/Developing Color Film/Developing
Overview
History
Black and White Film/Developing
Color Film/Developing

3. 1824, Joseph-Nicephore Niepce
First Permanent Image
“Heliogravure”
Asphalt on a Pewter Plate
Exposure took 5 days

4. 1839, Louis Daguerre “Daguerreotypes”
Sensitized Silver-plated Copper Sheet
Mercury-vapor developer

5. 1841, William Henry Fox Talbot
“Calotypes”
Salt Solution with Silver nitrate
Quicker Development/Lower Image Resolution

6. The Gelatine Emulsion 1881, George Eastman 1887, Hannibal Goodwin
Gelatin Dispersion of Silver-Halide
1887, Hannibal Goodwin
Plastic-backed “modern film”

7. The Chemistry of
Black and White Film

8. AgI >> AgBr >> AgCl
silver halide salts
AgI >> AgBr >> AgCl
Silver halides form imperfect crystals in the Dispersion
A photon of light may hit the crystal, exciting the electron on the negatively charged halide
The electron is transferred into the conduction band of the silver halide microcrystal at the sensitivity speck

9. Chemical engineer’s resource page www.cheresources.com/photochem
Image Formation
Chemical engineer’s resource page

10. The emulsion layer is ~12% silver halide
Grain size affects contrast and light sensitivity 0.1 ~ 3 microns
Anti-halation backing prevents reflections
More photons = more silver

11. Developer: Amplifies the Image
A reducing agent (Hydroquinone)
Sodium hydroxide and sodium carbonate added as accelerators
Potassium bromide added as restrainer
Reaction must be timed

12. Stop Bath Developers work at high pH
A weak acid (acetic acid) is used to halt the reaction

13. Fixer Sodium thiosulfate makes water soluble silver thiosulfate
Removes undeveloped silver halide crystals
Sodium thiosulfate makes water soluble silver thiosulfate
Photo paper is rinsed and dried

14. 1912, Rudolph Fischer's Dye Coupler Process
Color Film
1912, Rudolph Fischer's Dye Coupler Process

15. Color Film Silver halides only sensitive up to 525 nm
Coupling to dyes expands sensitivity range
Lower resolution than Black and White film
Latent images are black and white

16. Color Development paraphenylendiamine
Silver halide crystals are reduced by developer
Oxidized developer reacts with the dye couplers, activating the dye color
Printing paper has dye-coupled layers

17. History of Silver halide Chemistry
Summary
History of Silver halide Chemistry
B&W vs. Color Film

18. References
[1] Ian R. Gould et al Two-Electron Sensitization: A New Concept for Silver Halide Photography. J. Am. Chem. Soc., 122 (48), pp
[2] Tao Deng et al Fabrication of Metallic Microstructures Using Exposed, Developed Silver Halide-Based Photographic Film. Anal. Chem., 72 (4), pp
[3] Current, Ira. Photographic Color Printing: Theory and Technique. Copyright 1987, Butterworth Publishers.
[4] C. Swedlund. Photography. Copyright Holt, Rinehart, and Winston.
[5] The Chemical Engineer’s Resource Page. retrieved
[6] T. Naugler. University of Nova Scotia retrieved