Re: water treatments

[Ryuji Suzuki <rs@silvergrain.org>]

Sorry about the delayed response. I had a lot to do this past
weeks...

From: Bogdan Karasek <bkarasek@videotron.ca>
Subject: Re: water treatments (was Re: Agyrotype)
Date: Tue, 27 May 2008 17:58:36 -0400

> I am getting my act together to start making my own dry
> plates coated with my own emulsion.  What is this difference
> that you refer to????  I need some clarification here??? Is
> it better to use deionized water or distilled water?  I'm
> not sure which aspect of silver gelatin emulsion making you
> are referring to.

If you are limiting your interest to simple fine grain slow
emulsion (average grain size of 0.3 micron or less) then you
may not have much problem other than slightly higher level of
fog or perhaps pepper fog.

Problems with using non-pure water in emulsion making is that
your silver jet will contain irregular silver halide grains
that are spontaneously developable in developers.

For example, if you want to grow beautiful crystals of sugar,
salt, copper sulfate, whatever, the first thing you need is to
remove foreign material from the solution, and then control
the supersaturation of the bulk solution. It also helps to
form small crystals, pick good looking ones to use as the seed
crystals, then grow bigger crystals from them. The methods
applied in silver halide emulsion making is unique and
different (because of vast difference in the solubility), but
the principle is the same.

When you want larger crystals, these irregular grains formed
by impure chlorinated water can act as a host particle on
which the silver halide grows as you proceed in the nucleation
and growth stages. Usually, you want the kettle and jet to be
as clean and free of any foreign material as possible,
especially dusts and other insoluble material.

Speaking of undesirable grains, you also want to pay attention
to the shape of the nozzle of the jets, agitation, gelatin
type and concentration, pAg, and temperature profile. These
factors have a large influence on the crystal shapes, and
those grains having twinned planes that are not parallel are
known to cause problems, especially when you make emulsions of
larger than about 0.4 micron size. These grains grow
abnormally fast compared to the regular crystals, and they
cause fog. Single jet emulsions are praticularly rich of these
undesirable grains and I don't recommend single jets for high
speed plate emulsions. (Even double jets require careful
control of the above factors.)

Another kind of problems occur when you apply optimal sulfur
sensitization or sulfur plus gold sensitization, regardless of
the crystal size. With a bit of extension of development time,
the fog level rises to an unacceptable level very easily, if
the emulsion crystals are not very well formed. A considerable
amount of troubleshooting work is waiting for you. I'd keep
everything as clean as possible to make the later work
simpler.

I think the most useful skill you will acquire by perfecting
the art of silver gelatin emulsion making is critical analysis
and troubleshooting.  (This is actually true of a lot of
things I do.) A lot of times, you are dealing with things that
you cannot see (even if you use electron microscopy) and it is
also very important to use the theory as an integral part of
the analysis as well as troubleshooting.

--
Ryuji Suzuki
"The truth that I am seeking is in your missing file."
(Bob Dylan, Something's Burning Baby, 1985)