[alt-photo] Re: Collodio-Chloride and Collodion-Based Silver-Chloride Processes: Strontium-Chloride vs Sodium Chloride?

[Francesco Fragomeni]

Ryuji,

Thanks for your thoughts. You're words are right in line with my
assumptions. I'm no chemist but I have a basic understanding of what occurs
when making these types of emulsions and while various different salts may
have cause minor differences, I would assume that they are just that,
minor. From my understanding, when an emulsion of this type is sensitized
the NaCL and AgNO3 molecules exchange to produce silver-chloride (AgCl, the
sensitive agent) and a non-sensitive byproduct that is typically discarded
in the wash (sodium-nitrate, NaNO3). The only thing I can think of is that
the Strontium-Chloride exchanges with Silver-Nitrate to produce
Strontium-Nitrate which may lend itself to some specific color, perhaps a
more prominent red that makes toning changes more evident. This is in line
will what I've read, that Strontium lent a color that made toning easier to
see. I'm still not sure about the alcohol solubility thing.

-Francesco


On Thu, May 31, 2012 at 2:03 AM, Ryuji Suzuki <rs at silvergrain.org> wrote:

> I don't have experience with collodion process but in silver gelatin
> process, the counter ions in the halide jet don't matter, as long as they
> are alkaline metal or alkali earth metal ions, impurities are well
> controlled, and the molar concentrations are adjusted. Those cations are
> just wasted without participating in any reaction that forms silver halide
> crystals. If solubility in alcohol is a factor, that may be one thing, but
> then what alcohol concentration are you talking about? In silver gelatin,
> sodium, potassium, and sometimes ammonium ions are used. Ammonium ions have
> different effects on silver halide crystals in a pH-dependent manner, but
> Na and K are largely irrelevant (in most cases, they are removed from the
> emulsion before chemical sensitization phase).
>
> Emulsions that are used for printing out processes are very different from
> emulsions for developed out processes. Don't underestimate that difference.
>
> I also would not put too much emphasis on stuff written in old literature,
> unless you can validate the statement with modern science. Systematic
> research of how emulsion crystals are formed and what factors have
> influence, etc., had to wait for sensitive instrumental amplifiers,
> electron microscopes, and various laboratory equipment in the 20th century.
> If certain issues or terminology disappeared in later literature, it might
> be because the earlier debate became irrelevant under the light of new
> science. THere are countless examples like that.
>
> --
> Ryuji Suzuki
> "When you're finished changing, you're finished." (Benjamin Franklin)
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