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التقنيات المهنية المتقدمة ..
تحسين السلبية بالتكثيف ..
متى يتم التكثيف
IMPROVING THE NEGATIVE BY INTENSIFICATION
We have made the point time and again that the best prints are made from good negatives . While an expert printer can often do wonders in making acceptable prints from poor negatives , he will always do a better job if his negatives are perfect . However , no photographer can expect to get perfect negatives every time . There will be occasions when you will read your meter incorrectly and underexpose , or there will be insufficient light to permit correct exposure , or you will shoot with a lens aperture of f / 16 when you thought it was f / 8 , or when your developer reached the exhaustion point before you realized it . All of these errors will result in negatives that are too thin to print properly . The loss of density will usually be accompanied by a loss in contrast as well .
If the loss in density and contrast is not too serious , the best solution is to print the negative on a more contrasty grade of paper . Some paper brands come in as many as six grades of contrast , and the No. 6 paper will often give an acceptable print from a negative which is ordinarily considered hopeless . However , if the shadows , or at least the darker middle tones have some detail , it is possible to build up density and contrast in such areas by intensifying the negative . Please note the qualification we have made in the previous sentence intensification will build up an area that has some , if insufficient , detail - it will have no effect on an area which has no detail at all . Before you intensify a negative , study it carefully to be sure that there is some detail in the areas you want to build up . If there is none , you will be wasting your time .
You will realize the limitations of intensification if you understand that it is nothing more than a process of depositing another metal , such as chromium , on top of the silver particles of the negative image . By doubling the amount of metal which makes up the image , both density and contrast are increased .
Figure 1A thin flat negative caused by underdevelopment
ENORM Figure 2 The soft print made from the underdeveloped negative of Figure 1 .
Figure 3 The negative of Figure 1 was intensified to increase its contrast .
Figure 4 The print made from the negative of Figure 3 . Note its normal density and contrast .
WHEN TO INTENSIFY
In deciding whether intensification will improve a negative , remember two very important things : intensification always increases both contrast and density . Obviously , then , you would intensify a negative only when it is both too thin and too flat . If a negative is too thin but has the correct contrast or even too much contrast , intensification will make it worse . Lack of density in itself is not particularly undesirable . As a matter of fact , many photographers try to get the thinnest usable negative that will give them sufficient contrast . If a negative is too flat but is also too dense , it should not be intensified because this will increase density even further . The correct remedy is reduction .
If a negative is too flat and has normal density , a slight amount of intensification may not hurt , but it is often better to reduce it slightly first with a reducer that increases contrast , and then intensify it if it is still too flat .
CHROMIUM INTENSIFIER . There are quite a large number of intensifiers you can use , but this Assignment will discuss only one - chromium . This intensifier has been in use for many years and is thoroughly reliable . It is best to intensify the negative as soon as possible after it has been made - preferably just after washing . and before it has been dried .
The chromium intensifier has the following advantages :
1. It is available in package form .
2. It is reliable .
3. It is easy to use .
4. It can produce a wide range of intensification .
5. It can be repeated to increase density still further .
6. It gives the least increase in grain , so that it is particularly good for small negatives .
7. The intensified image is fairly permanent .
With the chromium intensifier , the negative is first bleached and then redeveloped . If you use a packaged formula , follow the directions closely , since . these vary to some degree with the actual formula used . If you prefer to mix your own , start with the bleach formula which is :
Stock Solution
Potassium bichromate 1/2 oz . 45 grams
Hydrochloric acid ( C.P. ) 1 oz . or 30 cc
Water to make 16 oz . 500 cc
Note : Concentrated hydrochloric acid is very corrosive , so use it very carefully when mixing the foregoing formula .
For use , take 1 part of stock solution to 10 parts of water .
First soak the negative in water for several minutes until it is thoroughly wet . If the negative has been handled a great deal , swab it with a wad of cotton under water to remove all surface dirt and fingerprints . Then immerse it in the bleach solution until the image is bleached to a light brown all the way through and no trace of black remains when you look at it from the back . After bleaching , wash thoroughly for twenty minutes in running water to remove all traces of the potassium bichromate .
Redevelop the bleached and washed negative under white light in any rapid non - staining developer . A good developer for this purpose is any standard paper developer diluted somewhat , such as D - 72 ( or Dektol ) diluted 1 : 3 . Do not use a fine grain developer because such a developer will reduce ( dissolve away ) the shadows .
After redevelopment , wash and dry as usual .
If the negative is still too thin after intensification , you can repeat the process . However , let the negative dry first . The bleaching solution softens the gelatin so that it may not stand up under two successive stages of intensification unless it has a chance to dry in between .
The chromium intensifier , as we have seen , works in two stages . In the first stage , the negative is immersed in a bleaching solution which converts the silver into a double compound of silver and chromium . This is reddish brown in color so that it is easy to tell when bleaching has been completed . In the second stage , this bleached image is blackened , usually by developing it in a normal paper developer so that the final result is a double image , one in silver and the other in chromium .
A negative to be intensified properly must be completely free from hypo . If you are not sure of any negative and suspect that it may not have been washed thoroughly , wash it for at least half an hour before you intensify it .
التقنيات المهنية المتقدمة ..
تحسين السلبية بالتكثيف ..
متى يتم التكثيف
IMPROVING THE NEGATIVE BY INTENSIFICATION
We have made the point time and again that the best prints are made from good negatives . While an expert printer can often do wonders in making acceptable prints from poor negatives , he will always do a better job if his negatives are perfect . However , no photographer can expect to get perfect negatives every time . There will be occasions when you will read your meter incorrectly and underexpose , or there will be insufficient light to permit correct exposure , or you will shoot with a lens aperture of f / 16 when you thought it was f / 8 , or when your developer reached the exhaustion point before you realized it . All of these errors will result in negatives that are too thin to print properly . The loss of density will usually be accompanied by a loss in contrast as well .
If the loss in density and contrast is not too serious , the best solution is to print the negative on a more contrasty grade of paper . Some paper brands come in as many as six grades of contrast , and the No. 6 paper will often give an acceptable print from a negative which is ordinarily considered hopeless . However , if the shadows , or at least the darker middle tones have some detail , it is possible to build up density and contrast in such areas by intensifying the negative . Please note the qualification we have made in the previous sentence intensification will build up an area that has some , if insufficient , detail - it will have no effect on an area which has no detail at all . Before you intensify a negative , study it carefully to be sure that there is some detail in the areas you want to build up . If there is none , you will be wasting your time .
You will realize the limitations of intensification if you understand that it is nothing more than a process of depositing another metal , such as chromium , on top of the silver particles of the negative image . By doubling the amount of metal which makes up the image , both density and contrast are increased .
Figure 1A thin flat negative caused by underdevelopment
ENORM Figure 2 The soft print made from the underdeveloped negative of Figure 1 .
Figure 3 The negative of Figure 1 was intensified to increase its contrast .
Figure 4 The print made from the negative of Figure 3 . Note its normal density and contrast .
WHEN TO INTENSIFY
In deciding whether intensification will improve a negative , remember two very important things : intensification always increases both contrast and density . Obviously , then , you would intensify a negative only when it is both too thin and too flat . If a negative is too thin but has the correct contrast or even too much contrast , intensification will make it worse . Lack of density in itself is not particularly undesirable . As a matter of fact , many photographers try to get the thinnest usable negative that will give them sufficient contrast . If a negative is too flat but is also too dense , it should not be intensified because this will increase density even further . The correct remedy is reduction .
If a negative is too flat and has normal density , a slight amount of intensification may not hurt , but it is often better to reduce it slightly first with a reducer that increases contrast , and then intensify it if it is still too flat .
CHROMIUM INTENSIFIER . There are quite a large number of intensifiers you can use , but this Assignment will discuss only one - chromium . This intensifier has been in use for many years and is thoroughly reliable . It is best to intensify the negative as soon as possible after it has been made - preferably just after washing . and before it has been dried .
The chromium intensifier has the following advantages :
1. It is available in package form .
2. It is reliable .
3. It is easy to use .
4. It can produce a wide range of intensification .
5. It can be repeated to increase density still further .
6. It gives the least increase in grain , so that it is particularly good for small negatives .
7. The intensified image is fairly permanent .
With the chromium intensifier , the negative is first bleached and then redeveloped . If you use a packaged formula , follow the directions closely , since . these vary to some degree with the actual formula used . If you prefer to mix your own , start with the bleach formula which is :
Stock Solution
Potassium bichromate 1/2 oz . 45 grams
Hydrochloric acid ( C.P. ) 1 oz . or 30 cc
Water to make 16 oz . 500 cc
Note : Concentrated hydrochloric acid is very corrosive , so use it very carefully when mixing the foregoing formula .
For use , take 1 part of stock solution to 10 parts of water .
First soak the negative in water for several minutes until it is thoroughly wet . If the negative has been handled a great deal , swab it with a wad of cotton under water to remove all surface dirt and fingerprints . Then immerse it in the bleach solution until the image is bleached to a light brown all the way through and no trace of black remains when you look at it from the back . After bleaching , wash thoroughly for twenty minutes in running water to remove all traces of the potassium bichromate .
Redevelop the bleached and washed negative under white light in any rapid non - staining developer . A good developer for this purpose is any standard paper developer diluted somewhat , such as D - 72 ( or Dektol ) diluted 1 : 3 . Do not use a fine grain developer because such a developer will reduce ( dissolve away ) the shadows .
After redevelopment , wash and dry as usual .
If the negative is still too thin after intensification , you can repeat the process . However , let the negative dry first . The bleaching solution softens the gelatin so that it may not stand up under two successive stages of intensification unless it has a chance to dry in between .
The chromium intensifier , as we have seen , works in two stages . In the first stage , the negative is immersed in a bleaching solution which converts the silver into a double compound of silver and chromium . This is reddish brown in color so that it is easy to tell when bleaching has been completed . In the second stage , this bleached image is blackened , usually by developing it in a normal paper developer so that the final result is a double image , one in silver and the other in chromium .
A negative to be intensified properly must be completely free from hypo . If you are not sure of any negative and suspect that it may not have been washed thoroughly , wash it for at least half an hour before you intensify it .
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