[pure-silver] Re: Where's the Silver?
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx, rgacpa@xxxxxxxxxxx
- Date: Thu, 09 Sep 2004 23:12:17 -0400 (EDT)
From: Bob Adler <rgacpa@xxxxxxxxxxx>
Subject: [pure-silver] Where's the Silver?
Date: Thu, 9 Sep 2004 19:18:23 -0700 (PDT)
> Sorry to ask such a novice question, but is there
> silver in the film emulsion, in the film development
> process, or in the printing process?
Do you want to know the long version or short version?
I can give you a long one so that you can make it short.
In film emulsion, crystals consist of very pure silver halides. This
is a mix of silver chloride, bromide, and iodide. A tiny fraction of
these crystals are carefully, intentionally incorporated impurities:
other metals, silver sulfide, and metallic silver. A single crystal of
1 micron diameter contains about 20 billion silver halides. The
metallic silver content is probably a couple silver atoms per site, and
several sites per crystal at most.
When the crystal is exposed to light, latent image is formed. Latent
image consists of tiny specks of metallic silver (produced by
photoelectrons), together with gold and silver sulfide. There specks
catalyze development reaction, where crystals with latent images are
converted to metallic silver grains that form image. In highly
optimized emulsions, less than five silver atoms in a latent image is
sufficient to render the entire grain (of some 20 billion silver
halides) developable. The required latent image size is the same
regardless of the crystal size. So larger crystals get larger
"chemical amplification" of the exposed "signal" due to development.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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