Graded paper

wrote:

Michael Gudzinowicz wrote:

The reason the paper emulsions use a very fine grain
compared to film, is to improve image density without
wasting silver. Very fine grains when developed
have better covering power.

Might that read; Very fine grains when finely developed have ...?
My understanding is that the processing ph affects grain size. The
lower the ph the finer the grain. So I'd think maximum density
in a print results from low ph processing.
I did an experiment with an RC paper developed in D-23 diluted
1:3. I was impressed by the black density. The print did need
more exposure than a similar carbonated Ansco 120. Dan

I don't recall data on paper grain size or coverage vs pH.

You might want to check my "solarization" reply and link to Yurow's
page through the chemigram link page. He lists a number of properties
that are related to grain size, color, etc. Metol really is not a fine
grain developing agent per se (hydroquinone is, BTW), and the deep
cool blacks are due to large grains. The exposure increase or a
long development time doesn't hurt.

With films, "grain" is related the holes between clumps of developed
grains, and non-uniformity of grain distribution due to clumping.
At low pH's, the hardeners in the emulsion are more stable, and
with high ionic strengths, emulsion swelling is diminished. That leads
to less grain clumping, and more even distribution ("smaller" holes).
High sulfite and metol causes the grains to develop as filaments (increasing
size) which also "fills" the holes.

The "warm tone" paper developers (fine developed grain size) often use
hydroquinone as the only agent, and activation requires a high pH. The
situation is different from film. Actually the paper that may have had
the best coverage or highest reflection density reading was warm tone
Portriga. Unfortunately, one couldn't take advantage of that fact, since
the densities were so high that the eye couldn't distinguish one black
from a deeper black.

My question concerns solely how various grades of paper are
maunfactured without showing significant color differences. I have not
identified a mechanism in the literature, Probably trade secrets.

Michael Gudzinowicz wrote:
wrote:

Michael Gudzinowicz wrote:

The reason the paper emulsions use a very fine grain
compared to film, is to improve image density without
wasting silver. Very fine grains when developed
have better covering power.

Might that read; Very fine grains when finely developed have ...?
My understanding is that the processing ph affects grain size. The
lower the ph the finer the grain. So I'd think maximum density
in a print results from low ph processing.
I did an experiment with an RC paper developed in D-23 diluted
1:3. I was impressed by the black density. The print did need
more exposure than a similar carbonated Ansco 120. Dan

I don't recall data on paper grain size or coverage vs pH.

You might want to check my "solarization" reply and link to Yurow's
page through the chemigram link page. He lists a number of properties
that are related to grain size, color, etc. Metol really is not a fine
grain developing agent per se (hydroquinone is, BTW), and the deep
cool blacks are due to large grains. The exposure increase or a
long development time doesn't hurt.

With films, "grain" is related the holes between clumps of developed
grains, and non-uniformity of grain distribution due to clumping.
At low pH's, the hardeners in the emulsion are more stable, and
with high ionic strengths, emulsion swelling is diminished. That leads
to less grain clumping, and more even distribution ("smaller" holes).
High sulfite and metol causes the grains to develop as filaments (increasing
size) which also "fills" the holes.

The "warm tone" paper developers (fine developed grain size) often use
hydroquinone as the only agent, and activation requires a high pH. The
situation is different from film. Actually the paper that may have had
the best coverage or highest reflection density reading was warm tone
Portriga. Unfortunately, one couldn't take advantage of that fact, since
the densities were so high that the eye couldn't distinguish one black
from a deeper black.

UC wrote:

My question concerns solely how various grades of paper are
maunfactured without showing significant color differences. I have not
identified a mechanism in the literature, Probably trade secrets.

I think it's already been covered... they use the same average grain
size but vary the distribution.

The details of crystal growth and ripening are trade secrets for a
particular paper, but quite a bit has been published.

Michael Gudzinowicz wrote:
UC wrote:

My question concerns solely how various grades of paper are
maunfactured without showing significant color differences. I have not
identified a mechanism in the literature, Probably trade secrets.

I think it's already been covered... they use the same average grain
size but vary the distribution.

OK.

I looked in Mees (From Dry Plates to Ektachrome Film) again last night,
and despite a wealth of information on every conceivable topic relating
to the manufacture of sensitized goods, this particular was not
disclosed.

I am writing a book about 35mm technique, and a short treatment of
grain size distribution is part of the discussion about how to get the
finest grain in 35mm work (which is not by using fine-grain developers,
by the way). By increasing exposure a little and decreasing development
a little, more small grains are developed and fewer large grains are
developed completely, giving fewer 'holes', which produces the grain we
see. Also, infectious development is reduced.

Would you care to review the manuscript?

Respond to:

uraniumcommittee
----
@
----
yahoo.com


The details of crystal growth and ripening are trade secrets for a
particular paper, but quite a bit has been published.

UC wrote:

By increasing exposure a little and decreasing development
a little, more small grains are developed and fewer large grains ...


In other words reduce the EI and development time for
finer grain. I'd think it as reasonable to reduce the ph. Ph has,
apart from the film itself, the single most influence on grain size.
Should not that hold for print emulsions as well? Dan

wrote:
UC wrote:

By increasing exposure a little and decreasing development
a little, more small grains are developed and fewer large grains ...


In other words reduce the EI and development time for
finer grain.

Correct. Increase exposure, reduce development.

I'd think it as reasonable to reduce the ph. Ph has,
apart from the film itself, the single most influence on grain size.
Should not that hold for print emulsions as well? Dan

Although ph is a factor, most film developers are fairly low in ph
compared to paper developers, so this is not as big a factor as you
might think.

"Michael Gudzinowicz" wrote in
message news:SaNKf.3554$0z.2033@trnddc01...
UC wrote:

How are the grades of graded paper made different in
contrast?

Grain size?

The simplest way would be through variation of the
distribution of grain
sizes. If you have a broad distribution, large grains
would be exposed
at lower light intensities than small grains, extending
the response (low contrast; long exposure scale). With a
very narrow size distribution,
you move toward an all-or-none effect, where a small
increase in exposure will completely expose the smallest
grains (high contrast grades; short exposure scale).

Additionally, the grains are chemically sensitized, and
I'd imagine
that there are patents related to that, blending, etc. as
well as trade
secrets.

If you want to change the contrast of high contrast paper
or lith film,
or extend the scale of pictorial film, the film or paper
may be treated
with a very dilute proportional reducer (ferricyanide)
prior to development.
That treatment lowers the "contrast" of the latent image
(actually it reverses
some of the exposure by removing latent silver centers).
That approach is
outlined in my reply at:

http://www.largeformatphotography.in...ic/505080.html

Richard may have more detailed information - I think he
has a reference books on emulsion making. I haven't looked
at that literature for a long time (decades).

I don't have anything reliable on emulsion making. I have
noticed that image color varied from grade to grade in some
of the older graded papers. By old I mean those of fifty
years ago. I think current papers use blended emulsions with
different sensitizing. There are also dopants that affect
the contrast, but I don't have details. One would have to
know much more chemistry than I do and go through fairly
recent journal articles and patent literature to find out
what current practices really are.


--
---
Richard Knoppow
Los Angeles, CA, USA