[Leica] Silver and the "latent image"

[Edward Caliguri <caliguri@rcn.com>]

Martin-
    Loaded question! I'd pick up a book by Leslie Strobel (not his View
Camera Book - although that's great too) or a Chemistry of Photography text.
    In a VERY small nutshell, Silver (or Ag) which is in a salt form,
crystaline, in the emulsion (nowadays they can control the thinness and
shape of these) is in it's charged +1 state (note that other metals, such as
palladium, platinum, etc. exhibit these properties as well). When light
strikes the silver, it elevates what's called it's outer shell electron, in
this +1 ion to yet one with a higher energy level, where it will like to
"sit" for a while - a long while (quantum mechanically this can be shown,
but not NOW :-) When a developer (or reducing agent) comes in contact with
it, that chemical (say ascorbate in XTOL) ii "hands it another electron to
take up that place currently used by our "elevated" electron. Since they
both cannot occupy the same place, one gets pushed back. BUT, our Ag+1 now
has had an electron added to it, and becomes "reduced" to silver metal -
More where more light hit the film, less where it did not!
How does that sit? 
    Ed

> From: Martin Howard <mvhoward@mac.com>
> Subject: [Leica] Latent images
> Message-ID: <46BCB4E3-A414-11D7-924D-000393802534@mac.com>
> References: 
> 
> How is the latent image produced in films?  What is the mechanism?
> 
> M.

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