[pure-silver] Re: Are most photographers visual learners... Sensitometry 101

  • From: "Dave V" <DValvo@xxxxxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Sun, 11 Nov 2007 09:13:12 -0500

Sensitometry 101

The way Kodak used to control the sensitized paper coating process (before sensitometry) was to make a print using a standard negative of a person. The fresh print was then visually compared to a set of standards. There was a standard print of each paper made for each surface. When sensitometry was introduced for paper systems, left over hand me downs, were provided from the "Film Division". But the transmission densitometers had to be modified for reflection system.

In the early 1960's a new type of densitometer was introduced for Kodak paper testing. It was called "Room Viewing" as opposed to 0/45 system. Anyone know what that is???

But when a sample of paper is taken from the coating machine it is so fresh the emulsion might come off the paper when it is processed. How did Kodak solve that problem?

Dave



----- Original Message ----- From: "Laurence Cuffe" <cuffe@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, November 11, 2007 12:25 AM
Subject: [pure-silver] Re: Are most photographers visual learners... a little OT



On Saturday, November 10, 2007, at 03:37PM, "Dave V" <DValvo@xxxxxxxxxxxxxxxx> wrote:
Sorry to mislead.  I will disclose answer later, was wondering if others
knew.

----- Original Message ----- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, November 10, 2007 3:28 PM
Subject: [pure-silver] Re: Are most photographers visual learners... a
little OT


A nice question.
Previous to 1900 I don't believe that the quality of plates was well controlled. My evidence for this is circumstantial and is based on the widespread prevalence of development by inspection, which allows one to compensate for limited errors in exposure. In addition to this the use of various reducing formulae to control the contrast characteristics of the negative also seems to have been widespread. In the 1870's Swann developed the dry plate process which was a trade secret until revealed by Bennet. Mr Eastmann read Bennets paper in the BJP and traveled to London where he was unimpressed by the state of the art English facility for coating plates, where it was all done by hand. Eastmann returned to the states where he developed a two layer process where the silver containing emulsion is coated onto a paper backing which was pre-coated with gelatin. The resultant combined coating could be striped from the paper backing and coated onto standard glass plates. The next substantial development was flexible transparent backing for the emulsion, presumably cellulose nitrate bu I dot know how this was coated.
How am I doing Prof Valvo?

All the best
Laurence Cuffe


----- Original Message ----- From: "Dave V" <DValvo@xxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, November 10, 2007 9:19 AM
Subject: [pure-silver] Re: Are most photographers visual learners... a
little OT


Becky, I'm sure I'm not typical of those that read this post. I have more
science background than photographic (trying to fix that in retirement).
I have a masters degree in Image Science from RIT and spent 36 years at EK from building photographic test systems to introducing new B&W papers. I
have taught the science side of photography to thousands of people (most
at Kodak) but also in 5 countries. You can't imagine how trilled I am in
retirement to finally shoot images for myself rather than test targets or
Shirley's.  (Whoops!  I just let a Kodak tidbit secret out of the bag.
The first Kodak female model's name was Shirley.  Every time someone
needed model images, Shirley was called.  And we called the process
....get some "Shirley's" on this new film or paper. When a new model came along, with a different face, she was still called Shirley. After almost
a hundred years of shooting tests and models there have been a lot of
Shirley's. )  You won't believe how boring it is to look at Shirley's.

The things Shannon is doing is using an instrument to measure density and a pencil to plot the results. A great learning experience and a lot more
precise than "looking " at an image..  Some people have listed the books
printed that describe the process.  That said.  Before Kodak introduced
sensitometry and densitometry does anyone know how the manufacturing
coating process was tested and controlled????

---------------------------------------
Do you know when Kodak began to use sensitometric testing? The basis of
the science is due to Hurter and Driffield. The citation is to their
paper:

Ferdnand Hurter and Vero Driffield, "Photochemical Investigations and a
New Method of Determination of the Sensitiveness of Photographic Plates",
The Journal of the Society of Chemical Industry, May 31, 1890

   Certainly Mees must have been cognizant of this but I wonder if GE or
anyone else at EKC was. Mees joined Kodak in 1912 but the principles of
H&D must have been known there earlier.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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