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التقنيات المهنية المتقدمة ..
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TYPES OF REDUCERS
Chemical reducers may be grouped into three types according to the effect they have on negative contrast . The three types are :
SUBTRACTIVE OR CUTTING REDUCERS . These remove an equal quantity of silver in the highlights , middle tones and shadows . Because of the noticeably reduced density in the shadow areas , the negative appears to have considerably greater contrast . Moreover , such thinner negatives have greater printing contrast with condenser enlargers so that there is a double increase in printing contrast .
Cutting reducers are particularly useful in correcting fogged negatives .
PROPORTIONAL REDUCERS . These work in such a way that the net result is a reduction in density , but the printing contrast of the negative remains substantially unaffected .
SUPER - PROPORTIONAL REDUCERS . These are quite active in dense areas , but are relatively inactive in areas of low density . They , therefore , not only reduce density , but decrease contrast as well . They are useful for overdeveloped negatives of very contrasty subjects .
SUBTRACTIVE ( CUTTING ) REDUCERS
This reducer , often called Farmer's reducer after its originator , Howard Farmer , is by far the most popular . It contains two ingredients , potassium ferricyanide and hypo . The potassium ferricyanide quickly attracts the silver image , oxidizing it to silver ferricyanide , which is then dissolved by the hypo .
A mixture of potassium ferricyanide and hypo deteriorates very rapidly and so must be prepared and stored in two separate stock solutions which are mixed just before use . The separate solutions will keep almost indefinitely if the ferricyanide is stored in the dark or in a brown bottle . Reduction will ordinarily take place within five minutes , but if the negative is very dense and requires longer treatment it may be necessary to transfer it to a fresh solution to avoid stain .
Farmer's reducer is so easily made that few photographers buy it ready . mixed . You do not need a chemical balance or scale to weigh out either the potassium ferricyanide or the hypo . Buy the ferricyanide in a one ounce or four ounce bottle so you know exactly how much you have without weighing it , and measure out the hypo by volume with your regular graduate . You will need a 10 % solution of potassium ferricyanide and a 25 % solution of hypo .
To make a 10 % solution of potassium ferricyanide , pour one ounce of it into about 8 ounces of water , stir thoroughly until all the crystals are dissolved and then add more water to give you a total volume of 10 ounces . You now have 1 oz . of ferricyanide in 10 oz . of solution , which is a 10 % solution .
To make a 25 % solution of hypo , pour 8 oz . of hypo crystals into 24 oz . or so of water , stir thoroughly until dissolved and add more water to bring the total volume to 32 oz . If you have no means of weighing out the 8 oz . of hypo , measure it by volume . The strength of the hypo solution is far from critical so that it need not be weighed out accurately .
Start by soaking the negative in a tray of water at room temperature for 5 to 10 minutes . Then swab both sides with a wad of cotton under water so as to remove all surface dirt , fingerprints , etc. , which it may have picked up .
While the negative is soaking , prepare a clean tray for the reducer solution . It is best to use a white tray so that the progress of reduction can be watched closely . If you use a steel enameled tray , be sure that it is perfectly clean and has no cracks . Any cracks in the porcelain will expose the bare steel and this will react with the reducing solution . If you find some deep blue spots on your negative , you will know that some iron got into the reducing solution .
When the negative is ready , mix the reducer and pour it into the tray . This is done as follows : Pour 1 oz . of the ferricyanide solution into a 32 oz . graduate . Then pour 4 oz . of the hypo solution into the same graduate . Finally , add plain water to make a total of 32 oz . Stir briefly until the solution is uniform and pour into the tray . Now insert the washed and cleaned negative , emulsion side up , and rock the tray gently to promote uniform action .
Pick up the film occasionally and look through it at some white object , such as a white card or the bottom of the tray , to note the progress of reduction . When the negative has been reduced sufficiently , wash and dry in the usual way .
PROPORTIONAL REDUCERS
Hypo - ferricyanide may be used to give almost completely proportional reduction if used as a two solution formula . The negative is first treated in the potassium ferricyanide solution for a specific length of time , depending upon the degree of reduction required . It is then transferred to the hypo solution for 5 minutes or so , then given a short wash . If the reduction is insufficient , the process is repeated until the desired density is attained . Finally , the negative is washed and dried in the usual way . The detailed instructions follow :
Set out two trays of the size needed to take your negatives . For large negatives , it is best to work with 8 x 10 trays , but for small negatives 5 x 7's will be adequate . The following proportions will be correct for 5 x 7 trays . Prepare a working solution of potassium ferricyanide by adding 1 oz . of the 10 % stock solution to 15 oz . of water to give a total of 16 oz . Pour this into the first tray .
The hypo stock solution is diluted 1 : 1 so take 8 oz . of this stock solution and add an equal volume of water . Pour this working solution into the second tray .
The negative should have been soaked and cleaned with a wad of cotton as described in the preceding section . Now drain it and immerse it for exactly 1 minute in the diluted ferricyanide solution . Drain quickly and transfer it to the hypo . The hypo solution works quite quickly , so that reduction will be complete in just a few seconds . Allow from 30 to 60 seconds to be on the safe side and examine the negative . If reduction is insufficient , wash the negative for two or three minutes and repeat the process . If the negative is extremely dense , you may have to repeat this procedure quite a few times , or you may find it more advisable to keep the negative in the ferricyanide a little longer the first time . Toward the end , however , do not exceed the one minute treatment or you may dissolve away important shadow details . Once this is done , the negative is beyond repair .
When the density is about right , leave the negative in the hypo solution for a full 5 minutes . Then wash and dry in the usual way .
SUPER - PROPORTIONAL REDUCERS
The super - proportional reducers rely on the rather unique property of acidified potassium persulfate attacking silver vigorously when there is a lot of it present , and with much less vigor when the deposit of silver is quite small . This , of course , reduces contrast .
A persulfate reducer is likely to be rather tricky and so it is necessary to watch its action carefully . It starts quite slowly , but picks up speed at an accelerated rate . When using a persulfate reducer , be sure to remove the negative from the solution before it has lost important shadow detail .
Because of the unstable nature of the persulfates , they may be very erratic in their behavior . One batch of reducer will work quite well , and the next very poorly if at all . Apparently , minor impurities effect its action to a considerable degree . To minimize these effects , observe the following precautions .
1. Use pure water . If you have trouble in duplicating results , try distilled water .
2. Keep the two stock solutions separate and mix only just before use .
3. Do not store stock solutions of persulfate for long periods of time . If you must keep stock solutions on hand , keep the persulfate solution away from excessive heat and light - it will not keep for more than two months at 75 ° F . even in brown bottles .
CAUTION : POTASSIUM PERSULFATE REDUCER
This reducer requires the use of concentrated sulphuric acid . This is an extremely corrosive acid and it is dangerous to use unless you have had at least high school chemistry and have been taught how to handle such corrosive acids .
In spite of its many drawbacks , a persulfate reducer can on occasion be extremely useful . We are , therefore , giving you the formula in the following paragraph with detailed instructions for its use .
PERSULFATE REDUCER
Avoirdupois ---- Metric
Water 32 oz . 1 liter
Potassium persulfate 2 oz 60 grams
Sulfuric acid 3/4 dram 3 cc
Caution : Always add sulfuric acid to the solution slowly , stirring constantly Otherwise the solution may boil and spatter acid , causing severe burns .
For use , take one part of the stock solution and add two parts of water .
Before being immersed in this persulfate reducer , the negative must be very thoroughly fixed in a fresh hardener - type fixing bath and then washed . If the negative has been dried , let it soak in water for about ten minutes and then immerse it in the reducing solution . Rock the tray all the time the negative is in it and in a few minutes take out the negative and hold it up against the light to see if it is sufficiently reduced .
If it is not sufficiently reduced , put it back into the solution and continue to rock the tray . As soon as the negative has been reduced sufficiently , rinse it for a few seconds . If it has been softened too much by the reducer , immerse it in the regular acid - hardening fixing bath for a few minutes and then wash it .
التقنيات المهنية المتقدمة ..
أنواع المخفضات ..
TYPES OF REDUCERS
Chemical reducers may be grouped into three types according to the effect they have on negative contrast . The three types are :
SUBTRACTIVE OR CUTTING REDUCERS . These remove an equal quantity of silver in the highlights , middle tones and shadows . Because of the noticeably reduced density in the shadow areas , the negative appears to have considerably greater contrast . Moreover , such thinner negatives have greater printing contrast with condenser enlargers so that there is a double increase in printing contrast .
Cutting reducers are particularly useful in correcting fogged negatives .
PROPORTIONAL REDUCERS . These work in such a way that the net result is a reduction in density , but the printing contrast of the negative remains substantially unaffected .
SUPER - PROPORTIONAL REDUCERS . These are quite active in dense areas , but are relatively inactive in areas of low density . They , therefore , not only reduce density , but decrease contrast as well . They are useful for overdeveloped negatives of very contrasty subjects .
SUBTRACTIVE ( CUTTING ) REDUCERS
This reducer , often called Farmer's reducer after its originator , Howard Farmer , is by far the most popular . It contains two ingredients , potassium ferricyanide and hypo . The potassium ferricyanide quickly attracts the silver image , oxidizing it to silver ferricyanide , which is then dissolved by the hypo .
A mixture of potassium ferricyanide and hypo deteriorates very rapidly and so must be prepared and stored in two separate stock solutions which are mixed just before use . The separate solutions will keep almost indefinitely if the ferricyanide is stored in the dark or in a brown bottle . Reduction will ordinarily take place within five minutes , but if the negative is very dense and requires longer treatment it may be necessary to transfer it to a fresh solution to avoid stain .
Farmer's reducer is so easily made that few photographers buy it ready . mixed . You do not need a chemical balance or scale to weigh out either the potassium ferricyanide or the hypo . Buy the ferricyanide in a one ounce or four ounce bottle so you know exactly how much you have without weighing it , and measure out the hypo by volume with your regular graduate . You will need a 10 % solution of potassium ferricyanide and a 25 % solution of hypo .
To make a 10 % solution of potassium ferricyanide , pour one ounce of it into about 8 ounces of water , stir thoroughly until all the crystals are dissolved and then add more water to give you a total volume of 10 ounces . You now have 1 oz . of ferricyanide in 10 oz . of solution , which is a 10 % solution .
To make a 25 % solution of hypo , pour 8 oz . of hypo crystals into 24 oz . or so of water , stir thoroughly until dissolved and add more water to bring the total volume to 32 oz . If you have no means of weighing out the 8 oz . of hypo , measure it by volume . The strength of the hypo solution is far from critical so that it need not be weighed out accurately .
Start by soaking the negative in a tray of water at room temperature for 5 to 10 minutes . Then swab both sides with a wad of cotton under water so as to remove all surface dirt , fingerprints , etc. , which it may have picked up .
While the negative is soaking , prepare a clean tray for the reducer solution . It is best to use a white tray so that the progress of reduction can be watched closely . If you use a steel enameled tray , be sure that it is perfectly clean and has no cracks . Any cracks in the porcelain will expose the bare steel and this will react with the reducing solution . If you find some deep blue spots on your negative , you will know that some iron got into the reducing solution .
When the negative is ready , mix the reducer and pour it into the tray . This is done as follows : Pour 1 oz . of the ferricyanide solution into a 32 oz . graduate . Then pour 4 oz . of the hypo solution into the same graduate . Finally , add plain water to make a total of 32 oz . Stir briefly until the solution is uniform and pour into the tray . Now insert the washed and cleaned negative , emulsion side up , and rock the tray gently to promote uniform action .
Pick up the film occasionally and look through it at some white object , such as a white card or the bottom of the tray , to note the progress of reduction . When the negative has been reduced sufficiently , wash and dry in the usual way .
PROPORTIONAL REDUCERS
Hypo - ferricyanide may be used to give almost completely proportional reduction if used as a two solution formula . The negative is first treated in the potassium ferricyanide solution for a specific length of time , depending upon the degree of reduction required . It is then transferred to the hypo solution for 5 minutes or so , then given a short wash . If the reduction is insufficient , the process is repeated until the desired density is attained . Finally , the negative is washed and dried in the usual way . The detailed instructions follow :
Set out two trays of the size needed to take your negatives . For large negatives , it is best to work with 8 x 10 trays , but for small negatives 5 x 7's will be adequate . The following proportions will be correct for 5 x 7 trays . Prepare a working solution of potassium ferricyanide by adding 1 oz . of the 10 % stock solution to 15 oz . of water to give a total of 16 oz . Pour this into the first tray .
The hypo stock solution is diluted 1 : 1 so take 8 oz . of this stock solution and add an equal volume of water . Pour this working solution into the second tray .
The negative should have been soaked and cleaned with a wad of cotton as described in the preceding section . Now drain it and immerse it for exactly 1 minute in the diluted ferricyanide solution . Drain quickly and transfer it to the hypo . The hypo solution works quite quickly , so that reduction will be complete in just a few seconds . Allow from 30 to 60 seconds to be on the safe side and examine the negative . If reduction is insufficient , wash the negative for two or three minutes and repeat the process . If the negative is extremely dense , you may have to repeat this procedure quite a few times , or you may find it more advisable to keep the negative in the ferricyanide a little longer the first time . Toward the end , however , do not exceed the one minute treatment or you may dissolve away important shadow details . Once this is done , the negative is beyond repair .
When the density is about right , leave the negative in the hypo solution for a full 5 minutes . Then wash and dry in the usual way .
SUPER - PROPORTIONAL REDUCERS
The super - proportional reducers rely on the rather unique property of acidified potassium persulfate attacking silver vigorously when there is a lot of it present , and with much less vigor when the deposit of silver is quite small . This , of course , reduces contrast .
A persulfate reducer is likely to be rather tricky and so it is necessary to watch its action carefully . It starts quite slowly , but picks up speed at an accelerated rate . When using a persulfate reducer , be sure to remove the negative from the solution before it has lost important shadow detail .
Because of the unstable nature of the persulfates , they may be very erratic in their behavior . One batch of reducer will work quite well , and the next very poorly if at all . Apparently , minor impurities effect its action to a considerable degree . To minimize these effects , observe the following precautions .
1. Use pure water . If you have trouble in duplicating results , try distilled water .
2. Keep the two stock solutions separate and mix only just before use .
3. Do not store stock solutions of persulfate for long periods of time . If you must keep stock solutions on hand , keep the persulfate solution away from excessive heat and light - it will not keep for more than two months at 75 ° F . even in brown bottles .
CAUTION : POTASSIUM PERSULFATE REDUCER
This reducer requires the use of concentrated sulphuric acid . This is an extremely corrosive acid and it is dangerous to use unless you have had at least high school chemistry and have been taught how to handle such corrosive acids .
In spite of its many drawbacks , a persulfate reducer can on occasion be extremely useful . We are , therefore , giving you the formula in the following paragraph with detailed instructions for its use .
PERSULFATE REDUCER
Avoirdupois ---- Metric
Water 32 oz . 1 liter
Potassium persulfate 2 oz 60 grams
Sulfuric acid 3/4 dram 3 cc
Caution : Always add sulfuric acid to the solution slowly , stirring constantly Otherwise the solution may boil and spatter acid , causing severe burns .
For use , take one part of the stock solution and add two parts of water .
Before being immersed in this persulfate reducer , the negative must be very thoroughly fixed in a fresh hardener - type fixing bath and then washed . If the negative has been dried , let it soak in water for about ten minutes and then immerse it in the reducing solution . Rock the tray all the time the negative is in it and in a few minutes take out the negative and hold it up against the light to see if it is sufficiently reduced .
If it is not sufficiently reduced , put it back into the solution and continue to rock the tray . As soon as the negative has been reduced sufficiently , rinse it for a few seconds . If it has been softened too much by the reducer , immerse it in the regular acid - hardening fixing bath for a few minutes and then wash it .
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