Re: Some points of ponder

"Oxidizing metallic silver particles won't result in the crystals of the
same
quality. (There may be a way to do it but it won't be simple.)"

At least such methods lead to the making of emulsions which were good enough
to record Lippmann photographs. I don't know how such methods would play out
with larger grains though. Why not give it a try?

When you bleach silver grains, you are likely to end up with mixed crystals.
E.g. if you use a copper halide bleach, you will get silver/copper crystals.
Thinking of the 1980s when silver prices skyrocketed, there has been some
research (and there are a couple of Kodak and Fuji patents) on the making of
silver/copper systems. So having to deal with that kind of emulsions is not
necessarily a disadvantage.

"Also, in order to make sufficiently light sensitive AgX crystals of
good developability, you need real tiny amount of impurities, defects,
etc. The method you mentioned didn't factor in the importance of these."

It may still be possible to introduce some "impurities" subsequently.

Martin

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>; <martinm@SoftHome.net>
Sent: Friday, July 16, 2004 9:24 PM
Subject: Re: Some points of ponder

> There are reasons why silver gelatin emulsions are made in the way
> they are, not the way you mentioned. AgX crystals are made from
> soluble halide and soluble silver salts. This allows to form crystals
> of high quality with little impurity and crystal defects. Oxidizing
> metallic silver particles won't result in the crystals of the same
> quality. (There may be a way to do it but it won't be simple.)
>
> Also, in order to make sufficiently light sensitive AgX crystals of
> good developability, you need real tiny amount of impurities, defects,
> etc. The method you mentioned didn't factor in the importance of these.
>
> One virtue of silver gelatin process is the development
> process. Although the concept of developing existed in Calotype
> process, this is most successfully used in silver gelatin process.
> Say we have films consisting of AgX crystals of 1 micron diameter.
> Each individual crystal has about 20 billion silver atoms. In
> non-developing processes like POP, much of these silver atoms must be
> reduced to silver by light exposure. This requires a lot of lot of
> light. In the case of silver gelatin, all that's needed is that as few
> as about 3 silver atoms be reduced by light exposure. Developer
> solution will reduce the rest of 20 billion atoms as long as the
> particular crystal has more than a couple of metallic silver atoms
> present. (that number, 3, is for film materials; typical paper
> materials need a few more silver atoms.) This makes chemical
> "amplification" factor of a few billions, and the material can
> register exposure by as few as several photons.
>
> You have to say bye bye to development and silver gelatin process if
> you try to incorporate more than 2 or so of silver atoms in individual
> crystals.
>
> --
> Ryuji Suzuki
> "You have to realize that junk is not the problem in and of itself.
> Junk is the symptom, not the problem."
> (Bob Dylan 1971; source: No Direction Home by Robert Shelton)
>
> From: MARTINM <martinm@SoftHome.net>
> Subject: Re: Some points of ponder
> Date: Fri, 16 Jul 2004 10:48:06 +0200
>
> > There are two things I would like to add to your very thorough
explanations:
> >
> > 1) Adding another dye to an already dye sensitized emulsion might turn
out
> > in practice to be difficult.
> > What about fully exposing and developing the film, applying a
rehalogenating
> > bleach and then re-sensitize in a IR dye bath?
> >
> > 2) Since colloidal silver is said to shift the sensitizing wavelength to
the
> > red and NIR (I think up to 800 nm or so), wouldn't it make sense to
slightly
> > pre-expose the emulsion and subsequently carry out colloidal
development?
> > The colloidal developer might be formed of a very diluted (say 1 : 100)
> > standard
> > developer.
> >
> > Martin
Received on Fri Jul 16 22:03:09 2004