Re: Introduction

[Steve Hodges <shodges@xxxxxxxxxxxxxx>]

George L Smyth wrote:
> 
> D76, for instance, contains sodium sulfite, which eats away at the edges of the
> grain clusters.

"In addition to its function as a preservative and prevention from
staining, sulphite has a third function.  It acts as a solvent for
silver halides and so promotes some physical development, which leads to
finer-grained images provided that its concentration is sufficiently
high".  (Jacobson, Ray & Attridge, The Manual of Photography, 1988,
p214)

Note that sulphite is a SILVER HALIDE solvent, not a SILVER solvent.

i.e. it acts more like a fixer than a bleach.

The sulphite slowly eats away silver halides.  This prevents some
aspects of infectious development that occur when crystal of AgH is
developed in close proximity to another.  It also allows activation
sites on crystals that may be deep within the crystal to be (eventually)
exposed to developer.

It actually has some similarities with monobath development.  Indeed,
both Sodium Sulphite, and Sodium Thiosulphate are described as "Silver
halide solvents".

Also note that what you see as grains in the image ARE NOT AgH grains,
but the random clumping of AgH grains.

Note that Sodium Sulphite (or sodium Metabisulphite) is a major
component in most developers (50 to 100g/l).  Notable exceptions are
high acutance developers

Steve
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