Re: Increasing Carbon speed.

From: Bill William <iodideshi@yahoo.co.jp>
Subject: Re: Increasing Carbon speed.
Date: Thu, 16 Dec 2004 20:52:22 +0900 (JST)

> It depends on the initial emulsion whether it is
> incredible or not. I doubt you would get that much
> increase with every emulsion.

Nothing is incredible. I'm just reinventing the wheel that was already
known to major manufacturers. I do see same degree of speed
increase with a fast plate emulsion. This emulsion is precipitated
very slowly at 70C and ripened, desalted and digested for high
sensitivity. This is sulfur plus gold sensitized. Cerium also worked
in other less sensitive emulsions that received short ripening,
desalting and sulfur only sensitization.

> I doubt that you would get 2 stops increase over
> sulfur+gold sensitisation.

The cerium doping paper I read did a number of measurements about
lifetime of photoelectrons, which is shortened with cerium dopant. I
take this data indicative of improved efficiency of forming latent
image centers. Main mechanism of gold sensitization is to improve
developability of small latent image centers. They work in different
mechanisms and I bet this is why they both work together in an
additive manner.

> Anyway, it is almost meaningless to describe results
> between emulsions of differing crystal size and habit.

Then you shouldn't ask about dopants. Many of them do something to the
electrical properties and crystallography of the crystals. What's nice
about cerium doping is that it enhances speed at the same time as
reducing crystal size.

> Well, there must be some inconsistency in your
> procedure... when things really are the same, it should be
> as predictable as clockwork.

As long as the material and formula are the same, emulsions come out
pretty much the same across batches. What I said is that the result
varies depending on the iodide content and time of addition of iodide.

> So far all I can figure out is that you wanted to make a
> simple unwashed chloride emulsion, probably a high speed
> version, with adequate contrast. You found your contrast
> was too low so you looked into the use of use of dopants

I get good contrast with desalted chloride emulsion. I just wanted a
simplified procedure to make very practical emulsion within one hour
so that I can make a batch with customized contrast every session.
These emulsions compare well with commercial multigrade enlarging
papers in terms of speed. These emulsions are pretty much done,
because I see no need to make them faster any more. (Exposure is
getting short even with 12x enlargement.) But this has nothing to do
with cerium. This uses another, much more common metal ion complex,
not rare earth.

> I am not sure you have to resort to using such unusual or
> left-field methods to attain suitable results.

So whatever you don't use is unusual and left-field method? Effect of
dopants are described in literature and patents as well. Out of many
enlarging papers that were discontinued in the past decade, several
chlorobromide emulsions had to be discontinued because good quality
could not be obtained without cadmium doping. Dopants have huge
influence in the photographic quality of emulsions and they are used
in products. My dopant is not cadmium but the effect is similar to
that obtained with cadmium.

> There is a lot of literature on Cerium salts in
> photothermography, and I have seen some work on cerium in
> color developer formulations as well... but I personally
> have not read any specifically dealing with cerium and
> ordinary chlorobromide emulsions. But then again, there
> are hundreds of thousands of papers and I have not seen
> them all!

As far as I know cerium is not used in chlorobromide emulsions. It is
used in iodobromide emulsions. But even then, I only saw one paper
which describes well on photographic and electrical properties of the
crystals but not at all on the method they used to prepare these
crystals. So some trial and error were necessary to take advantage of
this in my plate emulsions.

Anyway, if you don't want to describe your emulsions, that's fine.
I got enough information for what I need.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)