Re: bergger

From: permadocument <info@permadocument.be>
Subject: bergger
Date: Thu, 02 Feb 2006 09:12:12 +0100

> First of all, the different photographic emulsions are based on the original
> Guilleminot formulae so you do not have to be surprised by the superior
> quality of the fiber based emulsions. This is due to the fact that they
> contain more silver salts than the conventional photographic papers.

I appreciate your input, but I must disagree on this one. The image
quality and silver content are not directly linked.

FACT: Modern emulsion technology allows to achieve good density,
contrast and tonality with much less silver than old formulae.

I make emulsions of various types, and compared formulae from all era;
from 1920s German emulsions to tabular grain emulsions. Old emulsions
have a lot of "junk grains" that are not very sensitive to light and
therefore wasted without having themselves developed even in heavily
exposed areas. You see plenty of them in micrographs published by
famous Kodak researchers during 1940s and they are very easily
reproducible. On the other hand, modern emulsion technology makes
grains of very uniform sensitivity to minimize junk grains, thereby
improving the efficiency with which silver halide crystals are used to
build image density. Furthermore, with improved sensitization
technologies, we can get higher speed with smaller grains, and this
itself contributes to higher optical density with less silver coating
weight. This is because smaller metallic silver particles have higher
optical density than larger grains, per gram of silver per square
meter (smaller grains have higher covering power). Furthermore,
polymer blend and swelling control of gelatin have a large impact on
the image's Dmax, and so companies like Fuji and Kodak are working
very hard to come up with a polymer blend that allows sufficient
swelling without losing wet strength in developer.

Therefore, the fact that a product contains more silver means that the
production is based on inferior emulsion technology, inferior polymer
technology, or both.

Several writers openly criticized Eastman Kodak and other major
companies when they came up with tabular grain technology and other
means of using less silver in their products. Some people write for
well known magazines, and some others published well known darkroom
chemistry cookbook(s). I've spoken with some of those authors but they
knew nothing about emulsion technology. I don't understand why they
could publish such unsupported claims openly criticizing
manufacturers...

Amount of silver used in photographic film and paper is actually
smaller the better, provided that good image quality is obtained. In
general, you'll get better resolution and less chemical waste that
way.
Received on Thu Feb 2 03:41:48 2006