Image intensifiers

"sreenath" wrote in message
m...
hello all,

I have been reading about "image intensifiers". I have a
basic
question.

How is it possible to intensify an image after fixing has
been done?
Unless we actually make fresh(new) silver deposits on the
image, how
does the image get denser?

Also, some of the formulas specify that "the process can
be carried
out again and again till required intensification is
achieved".

The formula for chromium intensifier has potassium
dichromate and
hidrochloric acid. Does it convert the image silver to the
chloride
salt? If yes, in what way would it be different from using
any other
bleach that can also convert it to silver chloride?

Thanks,
Sreenath

Different intensifiers work in different ways. According
to Grant Haist (Modern Photographic Processing) Chromium
intensifier works by bleaching the metallic silver image to
silver chloride plus a chromium compound (not described) is
added to it. It is this additional chromium compound that
intensifies the image. When the bleached image is
redeveloped it consists of the metallic silver plus the
chromium. The process can be done two or three times. Each
time more chromium compound is added increasing the density
of the image. Chromium intensifier is essentially
proportional meaning it increases the contrast of the image.
It is relatively reliable and the resultant images are
relatively permanent.
Some toners can act as intensifiers, for instance Kodak
Rapid Selenium Toner will intensify. The degree of
intensification is low but the results are permanent and the
process is easily controlable. Bleach and redevelop Sepia
toner will also act as an intensifier provided the film is
well washed so that the bleach does not form Farmer's
reducer with the resiual hypo. Probably the image color has
some effect on the greater printing density.
Staining Pyro developers can also be used as
intensifiers. In effect, the Pyro stain image is an
intensifier. The image is bleached in a re-halogenating
bleach and redeveloped in Pyro.
At one time Mercury intensifiers were popular. They
produce a large degree of intensification. The drawback is
the highly poisonous nature of the ingredients and the lack
of permance of the image. Monckhoven's Intensifer was used
for the old screen half-tone process because it
simultaneously greatly increases the density of the dense
parts of the image and reduced the density of the low
density areas. This was useful for increasing the sharpness
of the dots. Monckhoven's uses Mercuric Cloride and
Potassium Cyanide. Luckily, it is not very useful for
general photography.
Modified versions of various toners have been used for
intensification, Uranium and Copper for example. Both add
some metal compound to the silver image as in the Chromium
intensifier. The images are not completely permanent as they
are not when these metal-ferricyanide solutions are used as
toners.
Intensfiers are interesting to play with and can
occasionally be useful but they also are risky. With the
exception of using KRST there is always a risk of damaging
the negative beyond salvation.
Because many variable contrast papers are capable of very
high contrast they can often be used to get an image from
film which may not seem to be printible. The disadvange of
this is that any blemish on the negative is much exagerated,
the virtue is that its safe.


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

Intensifiers can sometimes make poor negatives better but
they can't bring up detail that isn't there. An underexposed
negative just doesn't have anything in the darker shadows,
not enough light has struck the emulsion to be recorded. No
intensifier will help.

"sreenath" wrote in message
m...
hello all,

I have been reading about "image intensifiers". I have a
basic
question.

How is it possible to intensify an image after fixing has
been done?
Unless we actually make fresh(new) silver deposits on the
image, how
does the image get denser?

Also, some of the formulas specify that "the process can
be carried
out again and again till required intensification is
achieved".

The formula for chromium intensifier has potassium
dichromate and
hidrochloric acid. Does it convert the image silver to the
chloride
salt? If yes, in what way would it be different from using
any other
bleach that can also convert it to silver chloride?

Thanks,
Sreenath

Different intensifiers work in different ways. According
to Grant Haist (Modern Photographic Processing) Chromium
intensifier works by bleaching the metallic silver image to
silver chloride plus a chromium compound (not described) is
added to it. It is this additional chromium compound that
intensifies the image. When the bleached image is
redeveloped it consists of the metallic silver plus the
chromium. The process can be done two or three times. Each
time more chromium compound is added increasing the density
of the image. Chromium intensifier is essentially
proportional meaning it increases the contrast of the image.
It is relatively reliable and the resultant images are
relatively permanent.
Some toners can act as intensifiers, for instance Kodak
Rapid Selenium Toner will intensify. The degree of
intensification is low but the results are permanent and the
process is easily controlable. Bleach and redevelop Sepia
toner will also act as an intensifier provided the film is
well washed so that the bleach does not form Farmer's
reducer with the resiual hypo. Probably the image color has
some effect on the greater printing density.
Staining Pyro developers can also be used as
intensifiers. In effect, the Pyro stain image is an
intensifier. The image is bleached in a re-halogenating
bleach and redeveloped in Pyro.
At one time Mercury intensifiers were popular. They
produce a large degree of intensification. The drawback is
the highly poisonous nature of the ingredients and the lack
of permance of the image. Monckhoven's Intensifer was used
for the old screen half-tone process because it
simultaneously greatly increases the density of the dense
parts of the image and reduced the density of the low
density areas. This was useful for increasing the sharpness
of the dots. Monckhoven's uses Mercuric Cloride and
Potassium Cyanide. Luckily, it is not very useful for
general photography.
Modified versions of various toners have been used for
intensification, Uranium and Copper for example. Both add
some metal compound to the silver image as in the Chromium
intensifier. The images are not completely permanent as they
are not when these metal-ferricyanide solutions are used as
toners.
Intensfiers are interesting to play with and can
occasionally be useful but they also are risky. With the
exception of using KRST there is always a risk of damaging
the negative beyond salvation.
Because many variable contrast papers are capable of very
high contrast they can often be used to get an image from
film which may not seem to be printible. The disadvange of
this is that any blemish on the negative is much exagerated,
the virtue is that its safe.


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

Intensifiers can sometimes make poor negatives better but
they can't bring up detail that isn't there. An underexposed
negative just doesn't have anything in the darker shadows,
not enough light has struck the emulsion to be recorded. No
intensifier will help.

"Richard Knoppow" wrote in message
...
[...]
Because many variable contrast papers are capable of very
high contrast [...]

As high as the old Agfa #6?

"Richard Knoppow" wrote in message
...
[...]
Because many variable contrast papers are capable of very
high contrast [...]

As high as the old Agfa #6?

sreenath wrote:

hello all,

I have been reading about "image intensifiers". I have a basic
question.

How is it possible to intensify an image after fixing has been done?
Unless we actually make fresh(new) silver deposits on the image, how
does the image get denser?

Anything that increases density, whether by adding silver or by adding
something else that blocks light, will intensify an image. Bleaching,
to be useful, must be done with a bleach that converts the silver back
to halogen (which must then be either exposed or chemically fogged
before redevelopment). One can then redevelop with a staining developer
such as pyro, pyrocat, or coffee; one could develop in a color developer
mixed with color couplers to deposit dye around the silver as it redevelops.

Alternately, one could tone with a density adding toner such as selenium.

Also, some of the formulas specify that "the process can be carried
out again and again till required intensification is achieved".

This is typical for a toning type intensifier -- the basic treatment is
adding some density by toning image silver, effectively increasing the
size of each tiny silver grain so it blocks more light; if it's still
not dense enough, repeating the process will add still more metal to the
grain (even if the metal added isn't silver).

The formula for chromium intensifier has potassium dichromate and
hidrochloric acid. Does it convert the image silver to the chloride
salt? If yes, in what way would it be different from using any other
bleach that can also convert it to silver chloride?

This is exactly what happens -- dichromate with a chloride ion donor
will make silver chloride from image silver; redeveloping in the
intensifier then not only redevelops the silver, but deposits chromium
in an imagewise fashion; the process is repeatable because the chromium
doesn't bleach when the silver does (that is, the second bleaching won't
completely remove the image, even if you fix after bleaching, because
the chromium image would remain). There would be no difference from
using another bleach (ferricyanide, permangate, etc.) with hydrochloric
acid or sodium chloride as a chloride donor, followed by the same
fogging and redevelopment

--
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.

sreenath wrote:

hello all,

I have been reading about "image intensifiers". I have a basic
question.

How is it possible to intensify an image after fixing has been done?
Unless we actually make fresh(new) silver deposits on the image, how
does the image get denser?

Anything that increases density, whether by adding silver or by adding
something else that blocks light, will intensify an image. Bleaching,
to be useful, must be done with a bleach that converts the silver back
to halogen (which must then be either exposed or chemically fogged
before redevelopment). One can then redevelop with a staining developer
such as pyro, pyrocat, or coffee; one could develop in a color developer
mixed with color couplers to deposit dye around the silver as it redevelops.

Alternately, one could tone with a density adding toner such as selenium.

Also, some of the formulas specify that "the process can be carried
out again and again till required intensification is achieved".

This is typical for a toning type intensifier -- the basic treatment is
adding some density by toning image silver, effectively increasing the
size of each tiny silver grain so it blocks more light; if it's still
not dense enough, repeating the process will add still more metal to the
grain (even if the metal added isn't silver).

The formula for chromium intensifier has potassium dichromate and
hidrochloric acid. Does it convert the image silver to the chloride
salt? If yes, in what way would it be different from using any other
bleach that can also convert it to silver chloride?

This is exactly what happens -- dichromate with a chloride ion donor
will make silver chloride from image silver; redeveloping in the
intensifier then not only redevelops the silver, but deposits chromium
in an imagewise fashion; the process is repeatable because the chromium
doesn't bleach when the silver does (that is, the second bleaching won't
completely remove the image, even if you fix after bleaching, because
the chromium image would remain). There would be no difference from
using another bleach (ferricyanide, permangate, etc.) with hydrochloric
acid or sodium chloride as a chloride donor, followed by the same
fogging and redevelopment

--
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.

sreenath wrote:

hello all,

I have been reading about "image intensifiers". I have a basic
question.

How is it possible to intensify an image after fixing has been done?
Unless we actually make fresh(new) silver deposits on the image, how
does the image get denser?

Anything that increases density, whether by adding silver or by adding
something else that blocks light, will intensify an image. Bleaching,
to be useful, must be done with a bleach that converts the silver back
to halogen (which must then be either exposed or chemically fogged
before redevelopment). One can then redevelop with a staining developer
such as pyro, pyrocat, or coffee; one could develop in a color developer
mixed with color couplers to deposit dye around the silver as it redevelops.

Alternately, one could tone with a density adding toner such as selenium.

Also, some of the formulas specify that "the process can be carried
out again and again till required intensification is achieved".

This is typical for a toning type intensifier -- the basic treatment is
adding some density by toning image silver, effectively increasing the
size of each tiny silver grain so it blocks more light; if it's still
not dense enough, repeating the process will add still more metal to the
grain (even if the metal added isn't silver).

The formula for chromium intensifier has potassium dichromate and
hidrochloric acid. Does it convert the image silver to the chloride
salt? If yes, in what way would it be different from using any other
bleach that can also convert it to silver chloride?

This is exactly what happens -- dichromate with a chloride ion donor
will make silver chloride from image silver; redeveloping in the
intensifier then not only redevelops the silver, but deposits chromium
in an imagewise fashion; the process is repeatable because the chromium
doesn't bleach when the silver does (that is, the second bleaching won't
completely remove the image, even if you fix after bleaching, because
the chromium image would remain). There would be no difference from
using another bleach (ferricyanide, permangate, etc.) with hydrochloric
acid or sodium chloride as a chloride donor, followed by the same
fogging and redevelopment

--
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.

"jjs" wrote in message
...
"Richard Knoppow" wrote in
message
...
[...]
Because many variable contrast papers are capable of
very
high contrast [...]

As high as the old Agfa #6?

Yes. Remember that for years Agfa numbers were one digit
higher than other manufacturers, i.e., Agfa No.3 was the
same contrast as Kodak No.2. Modern Kodak and Agfa papers
with the maximum contrast filter are the equal of the old
papers. I've made prints with some sort of recongnizable
image from negatives which to the eye barely seemed to have
images on them. Not good prints, mind you, but a lot better
than I would have guessed possible.


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

"jjs" wrote in message
...
"Richard Knoppow" wrote in
message
...
[...]
Because many variable contrast papers are capable of
very
high contrast [...]

As high as the old Agfa #6?

Yes. Remember that for years Agfa numbers were one digit
higher than other manufacturers, i.e., Agfa No.3 was the
same contrast as Kodak No.2. Modern Kodak and Agfa papers
with the maximum contrast filter are the equal of the old
papers. I've made prints with some sort of recongnizable
image from negatives which to the eye barely seemed to have
images on them. Not good prints, mind you, but a lot better
than I would have guessed possible.


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