Developing film twice.

In article ,
no_name wrote:
Gregory L. Hansen wrote:

The local one-hour photo labs have very little ability to do special
requests like pushing film. And surely for good reason. But what would
happen if they just ran it through the developer machine twice? As I
recall, at some point it goes through a fixer bath that, well, fixes it,
and maybe it can't be developer further at all after that. But my
knowledge of the chemistry is really pretty sketchy.



Yup. Once it's fixed there ain't gonna be any more development.

Fixing removes the undeveloped silver from the film emulsion. Once you
do that, there's nothing to develop.

Silver? My knowledge of the chemistry really is pretty sketchy. I
thought they used light-sensitive dyes and that silver was old B&W stuff.


For B&W negatives, if they're a little underexposed, you can selenium
"tone" the negatives to give them a little more oomph.

Normally selenium toner is diluted 20:1. If you're going to tone the
negative, mix it at 3:1

What would happen if you just made a special instruction on the
mini-lab's bag and told them to process it as a higher speed film?
Process ISO 100 film as if it were ISO 200.

It's the same process for all film speeds. They pull a bit of film out of
the cartridge, tape it to a leader card, and insert it into the machine
and close the top. Then feed in the next while the first is still going
through the workings. There could be two films of different speeds taped
to the same leader, it doesn't matter, the timing and everything else is
the same.

--
"We don't grow up hearing stories around the camp fire anymore about
cultural figures. Instead we get them from books, TV or movies, so the
characters that today provide us a common language are corporate
creatures" -- Rebecca Tushnet

On 2005-12-14 21:07:25 -0500, (Gregory
L. Hansen) said:


Silver? My knowledge of the chemistry really is pretty sketchy. I
thought they used light-sensitive dyes and that silver was old B&W
stuff.

Of course there's silver. That's the light sensitive material. The dyes
are coupled.
--
Michael | "He's dead, Jim."

In article , Gregory L. Hansen
writes
In article ,
no_name wrote:
Gregory L. Hansen wrote:

The local one-hour photo labs have very little ability to do special
requests like pushing film. And surely for good reason. But what would
happen if they just ran it through the developer machine twice? As I
recall, at some point it goes through a fixer bath that, well, fixes it,
and maybe it can't be developer further at all after that. But my
knowledge of the chemistry is really pretty sketchy.



Yup. Once it's fixed there ain't gonna be any more development.

Fixing removes the undeveloped silver from the film emulsion. Once you
do that, there's nothing to develop.

Silver? My knowledge of the chemistry really is pretty sketchy. I
thought they used light-sensitive dyes and that silver was old B&W stuff.

To be accurate, it's not silver, but silver halides (mostly bromide,
with perhaps some chloride and iodide). Then, where light has hit one of
the grains, the action of developer is to reduce the silver bromide to
metallic silver, which is in very fine specks and thus appears black.
Silver bromide is soluble in fixer, whereas metallic silver is not
(well, actually it will dissolve, but only slowly, which is why fixing
time should not be over-extended).

This process forms the basis of almost all film and photographic
printing paper. Colour films use the action of the developer to deposit
coloured dyes and then remove the silver later, and use three (or more)
layers and filters to create the various colours, but the key
light-detection process always involves light-sensitive silver halide
and its reduction by a developer.

David
--
David Littlewood

In article ,
David Littlewood wrote:
In article , Gregory L. Hansen
writes
In article ,
no_name wrote:
Gregory L. Hansen wrote:

The local one-hour photo labs have very little ability to do special
requests like pushing film. And surely for good reason. But what would
happen if they just ran it through the developer machine twice? As I
recall, at some point it goes through a fixer bath that, well, fixes it,
and maybe it can't be developer further at all after that. But my
knowledge of the chemistry is really pretty sketchy.



Yup. Once it's fixed there ain't gonna be any more development.

Fixing removes the undeveloped silver from the film emulsion. Once you
do that, there's nothing to develop.

Silver? My knowledge of the chemistry really is pretty sketchy. I
thought they used light-sensitive dyes and that silver was old B&W stuff.

To be accurate, it's not silver, but silver halides (mostly bromide,
with perhaps some chloride and iodide). Then, where light has hit one of
the grains, the action of developer is to reduce the silver bromide to
metallic silver, which is in very fine specks and thus appears black.
Silver bromide is soluble in fixer, whereas metallic silver is not
(well, actually it will dissolve, but only slowly, which is why fixing
time should not be over-extended).

This process forms the basis of almost all film and photographic
printing paper. Colour films use the action of the developer to deposit
coloured dyes and then remove the silver later, and use three (or more)
layers and filters to create the various colours, but the key
light-detection process always involves light-sensitive silver halide
and its reduction by a developer.

Color film must have different silver-containing molecules that react to
one range of visible light but not others, and then latch on to one type
of dye but not the others.

After all this time, I wonder whether a better type of film (more light
sensitive, finer grain) can be made, but simply isn't because it couldn't
be developed in existing labs.


--
"Beer is living proof that God loves us and wants us to be happy."
-- Benjamin Franklin

In article , Gregory L. Hansen
writes

Color film must have different silver-containing molecules that react to
one range of visible light but not others, and then latch on to one type
of dye but not the others.

Well, kind of. There are 3 layers with different sensitivities to red,
green and blue light, but this is caused by organic sensitisers in the
silver halide crystals.

Very brief (and simplified) summary:

Top layer: unsensitised (and thus only sensitive to blue light
-----------
Yellow filter
-----------
Second layer: sensitised to green light, would record B + G but B
filtered out so records G only
-----------
Third layer: sensitised to red light, would record B + R but B filtered
out so records R only
-----------
Anti-halation coat (stops light bouncing back
-----------
Film base

The top layer contains colour couplers (organic molecules which react
with used developer to form dyes) which are yellow
The second layer contains couplers which (with used dev) form magenta
dye
The third layer contains couplers which form cyan dye.

Thus each layer records one colour and ends up as its complimentary one.

For more detail (and how this is extended to reversal film) I suggest a
little reading or web search. Note Kodachrome works somewhat
differently, but the principles are the same.

After all this time, I wonder whether a better type of film (more light
sensitive, finer grain) can be made, but simply isn't because it couldn't
be developed in existing labs.


The holy grail! In fact, it is quite impressive how much sensitivity and
grain have improved in the last 30 years.

David
--
David Littlewood

In article ,
David Littlewood wrote:
In article , Gregory L. Hansen
writes

Color film must have different silver-containing molecules that react to
one range of visible light but not others, and then latch on to one type
of dye but not the others.

Well, kind of. There are 3 layers with different sensitivities to red,
green and blue light, but this is caused by organic sensitisers in the
silver halide crystals.

Very brief (and simplified) summary:

Top layer: unsensitised (and thus only sensitive to blue light
-----------
Yellow filter
-----------
Second layer: sensitised to green light, would record B + G but B
filtered out so records G only
-----------
Third layer: sensitised to red light, would record B + R but B filtered
out so records R only
-----------
Anti-halation coat (stops light bouncing back
-----------
Film base

The top layer contains colour couplers (organic molecules which react
with used developer to form dyes) which are yellow
The second layer contains couplers which (with used dev) form magenta
dye
The third layer contains couplers which form cyan dye.

Thus each layer records one colour and ends up as its complimentary one.

Cool. Thanks.


For more detail (and how this is extended to reversal film) I suggest a
little reading or web search. Note Kodachrome works somewhat
differently, but the principles are the same.

After all this time, I wonder whether a better type of film (more light
sensitive, finer grain) can be made, but simply isn't because it couldn't
be developed in existing labs.


The holy grail! In fact, it is quite impressive how much sensitivity and
grain have improved in the last 30 years.

I don't know about grain, but 800 speed is still about as fast as film
seems to get unless you go to specialty suppliers. 1600 or 3200 just
doesn't seem to be carried by the local Ritz, Walgreens, or MotoPhoto.


--
"Did you know that most people use ten percent of their brains? I am now
one of them." -- Bart Simpson

Gregory L. Hansen wrote:

In article ,
no_name wrote:

Gregory L. Hansen wrote:


The local one-hour photo labs have very little ability to do special
requests like pushing film. And surely for good reason. But what would
happen if they just ran it through the developer machine twice? As I
recall, at some point it goes through a fixer bath that, well, fixes it,
and maybe it can't be developer further at all after that. But my
knowledge of the chemistry is really pretty sketchy.



Yup. Once it's fixed there ain't gonna be any more development.

Fixing removes the undeveloped silver from the film emulsion. Once you
do that, there's nothing to develop.


Silver? My knowledge of the chemistry really is pretty sketchy. I
thought they used light-sensitive dyes and that silver was old B&W stuff.


You could be right.

My experience with hand processing color is a little dated. I seem to
remember the silver in the emulsion held the dyes until development.
Once the image was developed and fixed, the silver was washed out to
leave the dyes behind.

David Littlewood wrote:

In article , Gregory L. Hansen
writes


Color film must have different silver-containing molecules that react to
one range of visible light but not others, and then latch on to one type
of dye but not the others.


Well, kind of. There are 3 layers with different sensitivities to red,
green and blue light, but this is caused by organic sensitisers in the
silver halide crystals.

Very brief (and simplified) summary:

Top layer: unsensitised (and thus only sensitive to blue light
-----------
Yellow filter
-----------
Second layer: sensitised to green light, would record B + G but B
filtered out so records G only
-----------
Third layer: sensitised to red light, would record B + R but B filtered
out so records R only
-----------
Anti-halation coat (stops light bouncing back
-----------
Film base

The top layer contains colour couplers (organic molecules which react
with used developer to form dyes) which are yellow
The second layer contains couplers which (with used dev) form magenta dye
The third layer contains couplers which form cyan dye.

Thus each layer records one colour and ends up as its complimentary one.

For more detail (and how this is extended to reversal film) I suggest a
little reading or web search. Note Kodachrome works somewhat
differently, but the principles are the same.


After all this time, I wonder whether a better type of film (more light
sensitive, finer grain) can be made, but simply isn't because it couldn't
be developed in existing labs.


The holy grail! In fact, it is quite impressive how much sensitivity and
grain have improved in the last 30 years.

David

Remember Kodak's Ektar films? Based IIRC on the T-grain developments
that gave T-Max, they had an Ektar 25 film that they touted as being the
color negative "equivalent" of Kodachrome 25.

The "grain" was as good, but there's no color negative film that really
had the color impact of Kodachrome.

OTOH, it was a whole lot more forgiving in its exposure latitude.