Photomechanical Process

Donald Qualls wrote:
Michael Scarpitti wrote:

No. The silver halide breaks down into metallic silver and halogen
when exposed to light. The gelatin holds the halogen away so it
cannot recombine with the silver. Developer amplifies this split. You
need to read more.


I doubt this, Michael. While this is the mechanism in a printing-out
processes like kallitype, it does not take place with developing-out
processes as used in modern films and papers, or occurs in such
miniscule quantity as to be undetectable even by tests like magnetic
resonance -- which has never been successfully used to detect an
undeveloped latent image. Reduced silver in the patter of the exposed
image, even in picogram quantities, would show up like a beacon in MRI.


I doubt MRI is sufficiently sensitive to detect two silver atoms on a
silver-halide grain. That is about the amount of silver deposited in a
latent image center (although more silver is better). Typically, more than
one development center is created on a normal silver-halide grain, but not
many compared to the number of silver-halide "molecules."

Michael Covington's explanation was correct, as far as is undertsood at
this time and allowing for the level of detail provided.

I do not believe so. I cannot imagine that exciting a silver halide
"molecule" to a higher energy state can possibly be the long-term
explanation for photographic effects. Recall that exposed undevelopped
films can be developped 40 years after exposure. When an atom is excited
to a higher energy state, say by reception of a quantum of energy, it does
not tend to stay in that state for days or weeks, much less years. The
random thermal actions in the material should undo that much quicker than
that. All the research I have read, both print-out and developing-out
latent images, indicate that the production of silver atoms (and
consequently free electrons, etc.) is the mechanism of the production of
the development centers.

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Donald Qualls wrote in message news:Z2tDc.187804$Ly.185307@attbi_s01...
Michael Scarpitti wrote:

No. The silver halide breaks down into metallic silver and halogen
when exposed to light. The gelatin holds the halogen away so it cannot
recombine with the silver. Developer amplifies this split. You need to
read more.

I doubt this, Michael.


Read 'The Science of Photography' before you say anything else. Siver
halides DO break down into silver and halogen (on a microsopic scale)
and this action makes the crystals developable. The halogen is trapped
by the gelatin, and improvements in latent image keeping properties of
emulsions derive from perfecting this.


While this is the mechanism in a printing-out
processes like kallitype, it does not take place with developing-out
processes as used in modern films and papers, or occurs in such
miniscule quantity as to be undetectable even by tests like magnetic
resonance -- which has never been successfully used to detect an
undeveloped latent image. Reduced silver in the patter of the exposed
image, even in picogram quantities, would show up like a beacon in MRI.

Developers fog because they're reducing unexposed silver, and
selectivity -- the ability of a developing agent to develop exposed
silver without reducing unexposed halide -- is a desirable trait; if
your proposed mechanism were responsible for latent image formation, a
developer would need only to be a reducing agent catalyzed by metallic
silver or a free halide radical -- and there would be little or no
advantage to the complex organic chemicals we use. Selectivity wouldn't
be an issue, because there wouldn't be any reduced silver in unexposed
areas.

Finally, if the gelatin is rigid enough on a molecular scale to keep
halogen from migrating and recombining with the silver, it would be too
rigid to allow the halogen radical to move away from the silver in the
first place, and recombination would be immediate.

Michael Covington's explanation was correct, as far as is undertsood at
this time and allowing for the level of detail provided.

--
I may be a scwewy wabbit, but I'm not going to Alcatwaz!
-- E. J. Fudd, 1954

Donald Qualls, aka The Silent Observer
Lathe Building Pages http://silent1.home.netcom.com/HomebuiltLathe.htm
Speedway 7x12 Lathe Pages http://silent1.home.netcom.com/my7x12.htm

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.

On Sat, 26 Jun 2004 09:28:32 -0400, Jean-David Beyer
wrote:

If that is what you meant, consider reading "The Theory Of The
Photographic Process", Third Edition, by Kenneth Mees and T.H.James.
Published by The Macmillan Company 1966. No ISBN: this was before ISBN
numbers. C.E.K.Mees was the head of Kodak's Research Department for many
years. George Eastman bought the company he worked for (Wrattan and
Wainright) in order to get him to work for Kodak.

Minor correction - the company was "Wratten and Wrainwright", which
was operating as Kodak UK after the takeover. The "Wratten" name
survived as a brand name for gelatin filters manufactured by Kodak,
according to a process invented by Wratten.

It is my opinion that no book as authoritative as that one will ever be
published again, unfortunately.

There is a 4th edition, which has Kenneth Mees dropped from the author
list. The first author is listed as T.H. James, and it was published
in 1977. According to Amazon, the ISBN number for that edition is
0023601906. I have seen (but unfortunately do not own) both editions.
As far as I remember, the 4th edition unfortunately omits the emulsion
making chapter, which arguably makes the 1966 vintage 3rd edition the
most valuable.

--
- Helge Nareid
Nordmann i utlendighet, Aberdeen, Scotland
For e-mail, please use my initials with the same domain as the posted address

Helge Nareid wrote:
On Sat, 26 Jun 2004 09:28:32 -0400, Jean-David Beyer
wrote:


If that is what you meant, consider reading "The Theory Of The
Photographic Process", Third Edition, by Kenneth Mees and T.H.James.
Published by The Macmillan Company 1966. No ISBN: this was before ISBN
numbers. C.E.K.Mees was the head of Kodak's Research Department for many
years. George Eastman bought the company he worked for (Wrattan and
Wainright) in order to get him to work for Kodak.


Minor correction - the company was "Wratten and Wrainwright", which
was operating as Kodak UK after the takeover. The "Wratten" name
survived as a brand name for gelatin filters manufactured by Kodak,
according to a process invented by Wratten.

It is my opinion that no book as authoritative as that one will ever be
published again, unfortunately.


There is a 4th edition, which has Kenneth Mees dropped from the author
list. The first author is listed as T.H. James, and it was published
in 1977. According to Amazon, the ISBN number for that edition is
0023601906. I have seen (but unfortunately do not own) both editions.
As far as I remember, the 4th edition unfortunately omits the emulsion
making chapter, which arguably makes the 1966 vintage 3rd edition the
most valuable.

I have only the 3rd edition. There is nothing specifically about emulsion
making in there. In Dr. Mees's preface to the earlier editions, he
apologizes for having nothing about emulsion making in there because
everything he knew about it (probably lots) he gained in confidence.

--
.~. Jean-David Beyer Registered Linux User 85642.
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/( )\ Shrewsbury, New Jersey http://counter.li.org
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On Sun, 18 Jul 2004 17:19:42 -0400, Jean-David Beyer
wrote:

Helge Nareid wrote:
On Sat, 26 Jun 2004 09:28:32 -0400, Jean-David Beyer
wrote:
There is a 4th edition, which has Kenneth Mees dropped from the author
list. The first author is listed as T.H. James, and it was published
in 1977. According to Amazon, the ISBN number for that edition is
0023601906. I have seen (but unfortunately do not own) both editions.
As far as I remember, the 4th edition unfortunately omits the emulsion
making chapter, which arguably makes the 1966 vintage 3rd edition the
most valuable.

I have only the 3rd edition. There is nothing specifically about emulsion
making in there. In Dr. Mees's preface to the earlier editions, he
apologizes for having nothing about emulsion making in there because
everything he knew about it (probably lots) he gained in confidence.

My recollection may well be wrong here. I remember an apology as you
describe in the 4th edition, but I thought it referred to that
particular edition alone. It is some years since I last read it, but I
seem to recall that it referred to the emulsion making section having
been removed for that edition. Not having easy access to university
libraries any longer, it is difficult for me to verify this. I am
currently looking for a copy of both editions, but since both are long
out of print, I am not at all sure that I will be able to get them.

--
- Helge Nareid
Nordmann i utlendighet, Aberdeen, Scotland
For e-mail, please use my initials with the same domain as the posted address

On Sun, 18 Jul 2004 17:19:42 -0400, Jean-David Beyer
wrote:

Helge Nareid wrote:
On Sat, 26 Jun 2004 09:28:32 -0400, Jean-David Beyer
wrote:
There is a 4th edition, which has Kenneth Mees dropped from the author
list. The first author is listed as T.H. James, and it was published
in 1977. According to Amazon, the ISBN number for that edition is
0023601906. I have seen (but unfortunately do not own) both editions.
As far as I remember, the 4th edition unfortunately omits the emulsion
making chapter, which arguably makes the 1966 vintage 3rd edition the
most valuable.

I have only the 3rd edition. There is nothing specifically about emulsion
making in there. In Dr. Mees's preface to the earlier editions, he
apologizes for having nothing about emulsion making in there because
everything he knew about it (probably lots) he gained in confidence.

My recollection may well be wrong here. I remember an apology as you
describe in the 4th edition, but I thought it referred to that
particular edition alone. It is some years since I last read it, but I
seem to recall that it referred to the emulsion making section having
been removed for that edition. Not having easy access to university
libraries any longer, it is difficult for me to verify this. I am
currently looking for a copy of both editions, but since both are long
out of print, I am not at all sure that I will be able to get them.

--
- Helge Nareid
Nordmann i utlendighet, Aberdeen, Scotland
For e-mail, please use my initials with the same domain as the posted address

Helge Nareid wrote (in part):
On Sun, 18 Jul 2004 17:19:42 -0400, Jean-David Beyer
wrote (in part):

I have only the 3rd edition. There is nothing specifically about emulsion
making in there. In Dr. Mees's preface to the earlier editions, he
apologizes for having nothing about emulsion making in there because
everything he knew about it (probably lots) he gained in confidence.


My recollection may well be wrong here. I remember an apology as you
describe in the 4th edition, but I thought it referred to that
particular edition alone. It is some years since I last read it, but I
seem to recall that it referred to the emulsion making section having
been removed for that edition. Not having easy access to university
libraries any longer, it is difficult for me to verify this. I am
currently looking for a copy of both editions, but since both are long
out of print, I am not at all sure that I will be able to get them.

From C.E.Kenneth Mees PREFACE TO THE FIRST EDITION (July 1942):

One omission in the book requires explanation. Abook on the theory of
photography should contain a chapter on emulsion making, discussing
various methods of procedure and their effect upon the finished product.
The author's knowledge of this subject has been acquired in confidence,
however, and he is not entitled to publish the material with the frankness
which alone would justify any publication.


So I think it was missing from the start. There is no such chapter in the
third edition, and, while I am aware that a fourth edition was published,
I have never seen it.

Amazon seem to have several used copies of the third and fourth edition

http://www.amazon.com/gp/product/off...?condition=all

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 20:35:00 up 2 days, 6:15, 3 users, load average: 4.02, 4.07, 4.02

On Sun, 18 Jul 2004 20:48:43 -0400, Jean-David Beyer
wrote:

Helge Nareid wrote (in part):
On Sun, 18 Jul 2004 17:19:42 -0400, Jean-David Beyer
wrote (in part):

I have only the 3rd edition. There is nothing specifically about emulsion
making in there. In Dr. Mees's preface to the earlier editions, he
apologizes for having nothing about emulsion making in there because
everything he knew about it (probably lots) he gained in confidence.


My recollection may well be wrong here. I remember an apology as you
describe in the 4th edition, but I thought it referred to that
particular edition alone. It is some years since I last read it, but I
seem to recall that it referred to the emulsion making section having
been removed for that edition. Not having easy access to university
libraries any longer, it is difficult for me to verify this. I am
currently looking for a copy of both editions, but since both are long
out of print, I am not at all sure that I will be able to get them.

From C.E.Kenneth Mees PREFACE TO THE FIRST EDITION (July 1942):

One omission in the book requires explanation. Abook on the theory of
photography should contain a chapter on emulsion making, discussing
various methods of procedure and their effect upon the finished product.
The author's knowledge of this subject has been acquired in confidence,
however, and he is not entitled to publish the material with the frankness
which alone would justify any publication.


So I think it was missing from the start. There is no such chapter in the
third edition, and, while I am aware that a fourth edition was published,
I have never seen it.

Thank you Jean-David. I read that apology in the 4th edition and
erroneously assumed that it only applied to that particular edition.


Amazon seem to have several used copies of the third and fourth edition

http://www.amazon.com/gp/product/off...?condition=all

I have managed to obtain a copy of the third edition through Amazon
(indirectly) - even though I have not received it yet, and I am
currently on the track of a copy of the 4th edition. I should warn
people that Amazon (at least amazon.uk) is not overly particular about
which edition they get you - I put in an order for the 4th edition and
got the 3rd. Since I want both editions anyway, that's all right, but
be warned.

I have also managed to source a copy of C.E.K. Mees' autobiography,
"From Dry Plates to Ektachrome Film", which I remember as an excellent
read. The seller said he is shipping it today.

--
- Helge Nareid
Nordmann i utlendighet, Aberdeen, Scotland
For e-mail, please use my initials with the same domain as the posted address