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Emulsion Geek #3: Optical/Spectral Sensitization vs. Chemical Sensitization, Part I

November 7, 2011

The term "sensitizer", as applied to photographic emulsions, can be confusing without the all-important modifiers "chemical" or "optical" (also called "spectral".) Chemical sensitizers are added to increase the speed of an emulsion; optical sensitizers are added to increase the sensitivity of an emulsion to selective wavelengths of light, or in the case of panchromatic film, to the entire spectrum of visible light.

There are books upon books upon papers written about emulsion sensitizers and how to use them. Here are a couple of good snippets —

From the Focal Encyclopedia of Photography, 1960 edition:


From Spectral Sensitization by Hans Meier, The Focal Press, 1968:


And, here's a great list. Many of these are available at Sigma Aldrich. I have purchased three, with little difficulty or fuss. I do have a business license, but I don't know if that makes a difference.

Continued in Part II here

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