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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. |
#2
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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. |
#3
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Image intensifiers
"Richard Knoppow" wrote in message
... [...] Because many variable contrast papers are capable of very high contrast [...] As high as the old Agfa #6? |
#4
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Image intensifiers
"Richard Knoppow" wrote in message
... [...] Because many variable contrast papers are capable of very high contrast [...] As high as the old Agfa #6? |
#5
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Image intensifiers
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. |
#6
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Image intensifiers
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. |
#7
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Image intensifiers
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. |
#8
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Image intensifiers
"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 |
#9
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Image intensifiers
"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 |
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