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#1
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NAACO Zip Fix
I picked up a gallon concentrate of Naaco Zip Fix the other day in my
local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry |
#2
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"LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. In fact, the acid of acid fixing baths probably has little effect on the stain image but may prevent overall staining. The retarding of washing from an acid fixer is eliminated when a sulfite wash aid, like Kodak Hypo Clearing Agent, is used following fixing. The wash aid also eliminates the binding of thiosulfate due to the mordanting effect of aluminum sulfate hardener. In color processing the acid may cause problems with the dye image, but the stain image from Pyro is not a dye. It is a pigment related to Humic acid, the stuff that makes wood brown. Nacco has been around for decades making low cost and entirely reliable products. I would just use the stuff as it is. -- --- Richard Knoppow Los Angeles, CA, USA |
#3
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"LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. In fact, the acid of acid fixing baths probably has little effect on the stain image but may prevent overall staining. The retarding of washing from an acid fixer is eliminated when a sulfite wash aid, like Kodak Hypo Clearing Agent, is used following fixing. The wash aid also eliminates the binding of thiosulfate due to the mordanting effect of aluminum sulfate hardener. In color processing the acid may cause problems with the dye image, but the stain image from Pyro is not a dye. It is a pigment related to Humic acid, the stuff that makes wood brown. Nacco has been around for decades making low cost and entirely reliable products. I would just use the stuff as it is. -- --- Richard Knoppow Los Angeles, CA, USA |
#4
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Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. |
#5
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Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. |
#6
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"Tom Phillips" wrote in message ... Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. There is some truth to this, but here is the story. Acid fixing baths can retard washing for two reasons, both of which are related to the pH. First, the pH of the gelatin decides the electrical charge of the molecules which in turn contolls the degree to which thiosulfate ions and ions of the reaction products are attracted to those molecules. Gelatin is peculiar because it is neither an acid or base but has characteristics of both. Such substances are known as amphoretic. Gelatin will take on the pH of the last solution it is treated with. However, gelatin has a characteristic which _is_ pH related and that is the pH at which the charges in it are at equilibrium. This is called the "isoelectric" point. The isoelectric point is also the point where the swelling of the gelatin when wet is minimum. For most photograhic gelatin the isoelectric point is slightly on the acid side of neutral. The isoelectric point is a function of the method by which the gelatin is refined. When the pH is below, that is on the acid side, of the isoelectric point, the charges are such that they tend to attract the thiosulfate ions. This is due to the familiar rule that opposing charges attract and similar charges repel. When the gelatin is brought to the alkaline side of the isoelectric point it will repel the thiosulfate ions and so they will wash out faster. Because photographic gelatin has an isoelectric point which is very slightly acid making it neutral in pH is sufficient to make the charges favorable to washing. The second reason acid fixers tend to retard fixing applies only to fixers containing Potassium aluminum sulfate, AKA White Alum, as a hardening agent. This substance hardens gelatin only over narrow range of pH which is somewhat on the acid side. The hardening action is destroyed if the emulsion is subsequently made alkaline. The alum also binds other substances to the gelatin molecules. This effect is described as being similar to the mordanting used to make dyes fast. At neutral pH the mordanting action no longer takes place but most of the hardening action is still effective. If the gelatin is made more alkaline, for instance by treating it in a 2% solution of Sodium carbonate or Sodium Metaborate (Kodalk) both the mordanting action and the hardening are destroyed. Hardeners are used in the fixing bath to prevent undue swelling of the emulsion in both fixing bath and subsequent washing. The gelatin is quite vulnerable to scratching and gouging when swollen. Newer films have emulsions which are thoroughly hardened in manufacture and probably do not need the further hardening of the fixing bath but some still do. The effect of these two binding forces on the thiosulfate ions and on the fixer reaction products (silver and thiosulfate complexes) is to extend washing times by perhaps three times. The effect of both binding actions can be eliminated if: 1, the gelatin is never made acid; 2, if it is not treated with alum hardener and left in an acid condition. A neutral or somewhat alkaline fixing bath accomplishes the first purpose and, indirectly, the second because an alum, or other metallic hardener, will not work in an alkaline environment. What is the disadvantage of a neutral or alkaline fixing bath? Mainly that any carried over developer remains active until either washed out or exhausted or enough halide is dissolved to prent further development. Secondly, an acid stop bath can not be used and in any case any developer in the emulsion would be reactivated in an alkaline fixer so it would do no good. If the fixing bath contains sulfite, which it must to preserve the thiosulfate, the developer will not produce stains due to oxidation products but it may make a difference in the final amount of development of the negatives. Usually in non-acid development systems, like some color films, an intermediate wash is used between development and fixation which is sufficient to wash out the bulk of the developer. The development time and this rinse time are calculated to result in the proper amount of development. This same thing can be done in black and white of course. Non acid processing is used for some color films becaue the dyes which make up the image are bleached or otherwise changed by the acid. What are the advantages of acidified fixer? First, development can be stopped at a definite point by using an acid stop bath and any carried over developer will not be reactivated in the fixing bath. However, the main reason for using acid fixers is to make possible the use of metallic hardening agents. Hardening was once absolutely necessary but has not been for some decades. Now, the saving grace is that the advantages of an alkaline or neutral fixer can be obtained even when using an acid, hardening, fixing bath, by the use of a correctly compounded Sodium sulfite wash aid. Kodak Hypo Clearing Agent is such a wash aid, and is the only one on the market AFAIK, which is compounded correctly to get the full advantage of adjustment of the emulsion to the critical pH where it is above the isoelectric point and above the point where alum hardener acts as a mordant but still at a pH where hardening is preserved. This is done by buffering the Sulfite to neutral pH with bisulfite. However, most of the ability of a sulfite wash aid to accelerate washing is due to a different mechanism, namely an ion exchange function of the sulfite itself. Sulfite tends to actively displace thiosulfate and silver complex ions from the emulsion. The sulfite ions are left in their places but are much more easily washed out. The use of a buffered Sulfite wash aid on film reduces the wash time by about a factor of six over that when a hardening acid fixer is used, and about three times the wash time of a non hardening fixer. Becuse of the ion exchange property wash time is even less than when a non-hardening neutral or alkaline fixer is used, perhaps by half. This ion exchange effect also takes place in the fibers of uncoated paper support (non RC printing paper) as well as in the emulsion. While the paper support does not wash out by a strictly diffusion process, as does the emulsion, the rate at which thiosulfate bound up in the fibers leaves during washing is still very considerably accelerated and wash times shortened to about one third of untreated prints. Buffering to neutral has two advantages over using a simple sulfite solution: it preserves hardening where that is desired; it places the gelatin close enough to its isoelectric point to minimise swelling thus resulting in the shortest diffusion path for the various ions which is its desired to wash out. Sulfite wash aid was developed from research into sea water washing. It has been known for over a century that sea water washes out film and paper considerably. However, the reason for this was not known until research into it was carried out during and after WW-2. Sea water washing was much used in practice during the war in locations where fresh water was at a premium such as on board ships at sea. Sea water washing requies a final rinse in fresh water to wash out the halides and other substances in the sea water which other wise will cause very rapid degration of the image. But, even with this rinse, there is a very consdierable saving in fresh water. Kodak Research Labs discovered that the salt most similar to sea water in accelerating washing was Sodium sulfite. Other sulfite salts work but not as well. some othe salts have accelerating effects but are well below sulfite in effectiveness. Kodak Labs also determined that the pH should be neutral, for the reasons mentioned. In addition to the Sulfite and bisulfite KHCA also contains two sequestering agents, EDTA Tetra sodium salt, and Sodium citrate, which bind up carbonates and prevent them from being deposited on the surface of the emulsion. This is mainly necessary when there is no rinse between an hardening fixing bath and the wash aid or when the wash aid is re-used. Sulfite wash aid also makes some otherwise insoluble fixer reaction products, or those tightly bound to the image silver, soluble. The effect of this is to extend fixer capacity because these products are left by partially exhausted fixing baths. Nonetheless, for good premanence fresh fixer should be used or a two bath fixer should be used. The point of all this is that fixer does not work any better when alkaline. The effectiveness of thoiosulfate (either sodium or ammonium) is not affected by the pH of the solution: it works equally well in acid, neutral, or alkaline solution. The only justification for a neutral fixer in B&W phtography might be the preservation of the stain image when using a Pyro developer, but I am not convinced that what people are seeing is not an increase in the overall stain (fog level) when doing this. The imagewise stain left by Pyro is NOT a dye but rather a quite tough pigment related to humic acid. This stain image, BTW, is probably more permanent than the silver image it accompanies. -- --- Richard Knoppow Los Angeles, CA, USA |
#7
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"Tom Phillips" wrote in message ... Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. There is some truth to this, but here is the story. Acid fixing baths can retard washing for two reasons, both of which are related to the pH. First, the pH of the gelatin decides the electrical charge of the molecules which in turn contolls the degree to which thiosulfate ions and ions of the reaction products are attracted to those molecules. Gelatin is peculiar because it is neither an acid or base but has characteristics of both. Such substances are known as amphoretic. Gelatin will take on the pH of the last solution it is treated with. However, gelatin has a characteristic which _is_ pH related and that is the pH at which the charges in it are at equilibrium. This is called the "isoelectric" point. The isoelectric point is also the point where the swelling of the gelatin when wet is minimum. For most photograhic gelatin the isoelectric point is slightly on the acid side of neutral. The isoelectric point is a function of the method by which the gelatin is refined. When the pH is below, that is on the acid side, of the isoelectric point, the charges are such that they tend to attract the thiosulfate ions. This is due to the familiar rule that opposing charges attract and similar charges repel. When the gelatin is brought to the alkaline side of the isoelectric point it will repel the thiosulfate ions and so they will wash out faster. Because photographic gelatin has an isoelectric point which is very slightly acid making it neutral in pH is sufficient to make the charges favorable to washing. The second reason acid fixers tend to retard fixing applies only to fixers containing Potassium aluminum sulfate, AKA White Alum, as a hardening agent. This substance hardens gelatin only over narrow range of pH which is somewhat on the acid side. The hardening action is destroyed if the emulsion is subsequently made alkaline. The alum also binds other substances to the gelatin molecules. This effect is described as being similar to the mordanting used to make dyes fast. At neutral pH the mordanting action no longer takes place but most of the hardening action is still effective. If the gelatin is made more alkaline, for instance by treating it in a 2% solution of Sodium carbonate or Sodium Metaborate (Kodalk) both the mordanting action and the hardening are destroyed. Hardeners are used in the fixing bath to prevent undue swelling of the emulsion in both fixing bath and subsequent washing. The gelatin is quite vulnerable to scratching and gouging when swollen. Newer films have emulsions which are thoroughly hardened in manufacture and probably do not need the further hardening of the fixing bath but some still do. The effect of these two binding forces on the thiosulfate ions and on the fixer reaction products (silver and thiosulfate complexes) is to extend washing times by perhaps three times. The effect of both binding actions can be eliminated if: 1, the gelatin is never made acid; 2, if it is not treated with alum hardener and left in an acid condition. A neutral or somewhat alkaline fixing bath accomplishes the first purpose and, indirectly, the second because an alum, or other metallic hardener, will not work in an alkaline environment. What is the disadvantage of a neutral or alkaline fixing bath? Mainly that any carried over developer remains active until either washed out or exhausted or enough halide is dissolved to prent further development. Secondly, an acid stop bath can not be used and in any case any developer in the emulsion would be reactivated in an alkaline fixer so it would do no good. If the fixing bath contains sulfite, which it must to preserve the thiosulfate, the developer will not produce stains due to oxidation products but it may make a difference in the final amount of development of the negatives. Usually in non-acid development systems, like some color films, an intermediate wash is used between development and fixation which is sufficient to wash out the bulk of the developer. The development time and this rinse time are calculated to result in the proper amount of development. This same thing can be done in black and white of course. Non acid processing is used for some color films becaue the dyes which make up the image are bleached or otherwise changed by the acid. What are the advantages of acidified fixer? First, development can be stopped at a definite point by using an acid stop bath and any carried over developer will not be reactivated in the fixing bath. However, the main reason for using acid fixers is to make possible the use of metallic hardening agents. Hardening was once absolutely necessary but has not been for some decades. Now, the saving grace is that the advantages of an alkaline or neutral fixer can be obtained even when using an acid, hardening, fixing bath, by the use of a correctly compounded Sodium sulfite wash aid. Kodak Hypo Clearing Agent is such a wash aid, and is the only one on the market AFAIK, which is compounded correctly to get the full advantage of adjustment of the emulsion to the critical pH where it is above the isoelectric point and above the point where alum hardener acts as a mordant but still at a pH where hardening is preserved. This is done by buffering the Sulfite to neutral pH with bisulfite. However, most of the ability of a sulfite wash aid to accelerate washing is due to a different mechanism, namely an ion exchange function of the sulfite itself. Sulfite tends to actively displace thiosulfate and silver complex ions from the emulsion. The sulfite ions are left in their places but are much more easily washed out. The use of a buffered Sulfite wash aid on film reduces the wash time by about a factor of six over that when a hardening acid fixer is used, and about three times the wash time of a non hardening fixer. Becuse of the ion exchange property wash time is even less than when a non-hardening neutral or alkaline fixer is used, perhaps by half. This ion exchange effect also takes place in the fibers of uncoated paper support (non RC printing paper) as well as in the emulsion. While the paper support does not wash out by a strictly diffusion process, as does the emulsion, the rate at which thiosulfate bound up in the fibers leaves during washing is still very considerably accelerated and wash times shortened to about one third of untreated prints. Buffering to neutral has two advantages over using a simple sulfite solution: it preserves hardening where that is desired; it places the gelatin close enough to its isoelectric point to minimise swelling thus resulting in the shortest diffusion path for the various ions which is its desired to wash out. Sulfite wash aid was developed from research into sea water washing. It has been known for over a century that sea water washes out film and paper considerably. However, the reason for this was not known until research into it was carried out during and after WW-2. Sea water washing was much used in practice during the war in locations where fresh water was at a premium such as on board ships at sea. Sea water washing requies a final rinse in fresh water to wash out the halides and other substances in the sea water which other wise will cause very rapid degration of the image. But, even with this rinse, there is a very consdierable saving in fresh water. Kodak Research Labs discovered that the salt most similar to sea water in accelerating washing was Sodium sulfite. Other sulfite salts work but not as well. some othe salts have accelerating effects but are well below sulfite in effectiveness. Kodak Labs also determined that the pH should be neutral, for the reasons mentioned. In addition to the Sulfite and bisulfite KHCA also contains two sequestering agents, EDTA Tetra sodium salt, and Sodium citrate, which bind up carbonates and prevent them from being deposited on the surface of the emulsion. This is mainly necessary when there is no rinse between an hardening fixing bath and the wash aid or when the wash aid is re-used. Sulfite wash aid also makes some otherwise insoluble fixer reaction products, or those tightly bound to the image silver, soluble. The effect of this is to extend fixer capacity because these products are left by partially exhausted fixing baths. Nonetheless, for good premanence fresh fixer should be used or a two bath fixer should be used. The point of all this is that fixer does not work any better when alkaline. The effectiveness of thoiosulfate (either sodium or ammonium) is not affected by the pH of the solution: it works equally well in acid, neutral, or alkaline solution. The only justification for a neutral fixer in B&W phtography might be the preservation of the stain image when using a Pyro developer, but I am not convinced that what people are seeing is not an increase in the overall stain (fog level) when doing this. The imagewise stain left by Pyro is NOT a dye but rather a quite tough pigment related to humic acid. This stain image, BTW, is probably more permanent than the silver image it accompanies. -- --- Richard Knoppow Los Angeles, CA, USA |
#8
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Richard Knoppow wrote:
"Tom Phillips" wrote in message ... Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. There is some truth to this, but here is the story. Acid fixing baths can retard washing for two reasons, both of which are related to the pH. First, the pH of the gelatin decides the electrical charge of the molecules which in turn contolls the degree to which thiosulfate ions and ions of the reaction products are attracted to those molecules. Gelatin is peculiar because it is neither an acid or base but has characteristics of both. Such substances are known as amphoretic. Gelatin will take on the pH of the last solution it is treated with. However, gelatin has a characteristic which _is_ pH related and that is the pH at which the charges in it are at equilibrium. This is called the "isoelectric" point. The isoelectric point is also the point where the swelling of the gelatin when wet is minimum. For most photograhic gelatin the isoelectric point is slightly on the acid side of neutral. The isoelectric point is a function of the method by which the gelatin is refined. When the pH is below, that is on the acid side, of the isoelectric point, the charges are such that they tend to attract the thiosulfate ions. This is due to the familiar rule that opposing charges attract and similar charges repel. When the gelatin is brought to the alkaline side of the isoelectric point it will repel the thiosulfate ions and so they will wash out faster. Because photographic gelatin has an isoelectric point which is very slightly acid making it neutral in pH is sufficient to make the charges favorable to washing. The second reason acid fixers tend to retard fixing applies only to fixers containing Potassium aluminum sulfate, AKA White Alum, as a hardening agent. This substance hardens gelatin only over narrow range of pH which is somewhat on the acid side. The hardening action is destroyed if the emulsion is subsequently made alkaline. The alum also binds other substances to the gelatin molecules. This effect is described as being similar to the mordanting used to make dyes fast. At neutral pH the mordanting action no longer takes place but most of the hardening action is still effective. If the gelatin is made more alkaline, for instance by treating it in a 2% solution of Sodium carbonate or Sodium Metaborate (Kodalk) both the mordanting action and the hardening are destroyed. Hardeners are used in the fixing bath to prevent undue swelling of the emulsion in both fixing bath and subsequent washing. The gelatin is quite vulnerable to scratching and gouging when swollen. Newer films have emulsions which are thoroughly hardened in manufacture and probably do not need the further hardening of the fixing bath but some still do. The effect of these two binding forces on the thiosulfate ions and on the fixer reaction products (silver and thiosulfate complexes) is to extend washing times by perhaps three times. The effect of both binding actions can be eliminated if: 1, the gelatin is never made acid; 2, if it is not treated with alum hardener and left in an acid condition. A neutral or somewhat alkaline fixing bath accomplishes the first purpose and, indirectly, the second because an alum, or other metallic hardener, will not work in an alkaline environment. What is the disadvantage of a neutral or alkaline fixing bath? Mainly that any carried over developer remains active until either washed out or exhausted or enough halide is dissolved to prent further development. Secondly, an acid stop bath can not be used and in any case any developer in the emulsion would be reactivated in an alkaline fixer so it would do no good. If the fixing bath contains sulfite, which it must to preserve the thiosulfate, the developer will not produce stains due to oxidation products but it may make a difference in the final amount of development of the negatives. Usually in non-acid development systems, like some color films, an intermediate wash is used between development and fixation which is sufficient to wash out the bulk of the developer. The development time and this rinse time are calculated to result in the proper amount of development. This same thing can be done in black and white of course. Non acid processing is used for some color films becaue the dyes which make up the image are bleached or otherwise changed by the acid. What are the advantages of acidified fixer? First, development can be stopped at a definite point by using an acid stop bath and any carried over developer will not be reactivated in the fixing bath. However, the main reason for using acid fixers is to make possible the use of metallic hardening agents. Hardening was once absolutely necessary but has not been for some decades. Now, the saving grace is that the advantages of an alkaline or neutral fixer can be obtained even when using an acid, hardening, fixing bath, by the use of a correctly compounded Sodium sulfite wash aid. Kodak Hypo Clearing Agent is such a wash aid, and is the only one on the market AFAIK, which is compounded correctly to get the full advantage of adjustment of the emulsion to the critical pH where it is above the isoelectric point and above the point where alum hardener acts as a mordant but still at a pH where hardening is preserved. This is done by buffering the Sulfite to neutral pH with bisulfite. However, most of the ability of a sulfite wash aid to accelerate washing is due to a different mechanism, namely an ion exchange function of the sulfite itself. Sulfite tends to actively displace thiosulfate and silver complex ions from the emulsion. The sulfite ions are left in their places but are much more easily washed out. The use of a buffered Sulfite wash aid on film reduces the wash time by about a factor of six over that when a hardening acid fixer is used, and about three times the wash time of a non hardening fixer. Becuse of the ion exchange property wash time is even less than when a non-hardening neutral or alkaline fixer is used, perhaps by half. This ion exchange effect also takes place in the fibers of uncoated paper support (non RC printing paper) as well as in the emulsion. While the paper support does not wash out by a strictly diffusion process, as does the emulsion, the rate at which thiosulfate bound up in the fibers leaves during washing is still very considerably accelerated and wash times shortened to about one third of untreated prints. Buffering to neutral has two advantages over using a simple sulfite solution: it preserves hardening where that is desired; it places the gelatin close enough to its isoelectric point to minimise swelling thus resulting in the shortest diffusion path for the various ions which is its desired to wash out. Sulfite wash aid was developed from research into sea water washing. It has been known for over a century that sea water washes out film and paper considerably. However, the reason for this was not known until research into it was carried out during and after WW-2. Sea water washing was much used in practice during the war in locations where fresh water was at a premium such as on board ships at sea. Sea water washing requies a final rinse in fresh water to wash out the halides and other substances in the sea water which other wise will cause very rapid degration of the image. But, even with this rinse, there is a very consdierable saving in fresh water. Kodak Research Labs discovered that the salt most similar to sea water in accelerating washing was Sodium sulfite. Other sulfite salts work but not as well. some othe salts have accelerating effects but are well below sulfite in effectiveness. Kodak Labs also determined that the pH should be neutral, for the reasons mentioned. In addition to the Sulfite and bisulfite KHCA also contains two sequestering agents, EDTA Tetra sodium salt, and Sodium citrate, which bind up carbonates and prevent them from being deposited on the surface of the emulsion. This is mainly necessary when there is no rinse between an hardening fixing bath and the wash aid or when the wash aid is re-used. Sulfite wash aid also makes some otherwise insoluble fixer reaction products, or those tightly bound to the image silver, soluble. The effect of this is to extend fixer capacity because these products are left by partially exhausted fixing baths. Nonetheless, for good premanence fresh fixer should be used or a two bath fixer should be used. The point of all this is that fixer does not work any better when alkaline. The effectiveness of thoiosulfate (either sodium or ammonium) is not affected by the pH of the solution: it works equally well in acid, neutral, or alkaline solution. The only justification for a neutral fixer in B&W phtography might be the preservation of the stain image when using a Pyro developer, but I am not convinced that what people are seeing is not an increase in the overall stain (fog level) when doing this. The imagewise stain left by Pyro is NOT a dye but rather a quite tough pigment related to humic acid. This stain image, BTW, is probably more permanent than the silver image it accompanies. I think I'm the one that got Richard started on this discourse, and I'm very grateful that he has taken the time to give such a clear and knowledgeable explanation of some fairly complex (to us English-major types trying to be "bathroom chemists") chemical reactions. Very helpful! One follow-up, Richard: I've been using Heico's "Permawash" for years as a washing aid. How does it compare with Kodak's Hypo Clearing Agent? Larry |
#9
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Richard Knoppow wrote:
"Tom Phillips" wrote in message ... Richard Knoppow wrote: "LR Kalajainen" wrote in message ... I picked up a gallon concentrate of Naaco Zip Fix the other day in my local camera store. Anyone heard of this? The concentrate was considerably cheaper than Ilford Rapid Fix. It lists only Ammonium Chloride and Metabisulfite as the ingredients. I'm guessing that I could make an alkaline fixer out of it with the addition of some metaborate or carbonate. The strength of the concentrate appears to be the same as Ilford's Rapid Fix, since it recommends the same dilutions for film and paper strengths. Will report on my experiments if I ever get time to get into the darkroom. Larry I don't have specific information about this fixer but most Nacco products are conventional, more or less generic versions of name brand products who's formulas are in the public domain. Rapid fixers are essentially identical to standard fixers other than containing Ammonium thiosulfate rather than Sodium thiosulfate. Ammonium chloride can be used in combination with Sodium thiosulfate to obtain a type of rapid fixer. Metabisulfite in solution is the equivalent of sulfite and an acid. I don't think its practical to convert this to an alkaline solution. You would have to neutralize the acid plus there might be undesirable reactions. If you want a neutral or alkaline fixer try any of the rapid fixers sold for color processing like Agfa Universal Fixer. These are non-hardening fixing baths of about neutral pH. They can be made alkaline by adding a small amount of sodium carbonate or metaborate. About the only reason for using an alkaline fixer is to maintain the stain image when using Pyro or Pyrochatichin developers. Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. There is some truth to this, but here is the story. Acid fixing baths can retard washing for two reasons, both of which are related to the pH. First, the pH of the gelatin decides the electrical charge of the molecules which in turn contolls the degree to which thiosulfate ions and ions of the reaction products are attracted to those molecules. Gelatin is peculiar because it is neither an acid or base but has characteristics of both. Such substances are known as amphoretic. Gelatin will take on the pH of the last solution it is treated with. However, gelatin has a characteristic which _is_ pH related and that is the pH at which the charges in it are at equilibrium. This is called the "isoelectric" point. The isoelectric point is also the point where the swelling of the gelatin when wet is minimum. For most photograhic gelatin the isoelectric point is slightly on the acid side of neutral. The isoelectric point is a function of the method by which the gelatin is refined. When the pH is below, that is on the acid side, of the isoelectric point, the charges are such that they tend to attract the thiosulfate ions. This is due to the familiar rule that opposing charges attract and similar charges repel. When the gelatin is brought to the alkaline side of the isoelectric point it will repel the thiosulfate ions and so they will wash out faster. Because photographic gelatin has an isoelectric point which is very slightly acid making it neutral in pH is sufficient to make the charges favorable to washing. The second reason acid fixers tend to retard fixing applies only to fixers containing Potassium aluminum sulfate, AKA White Alum, as a hardening agent. This substance hardens gelatin only over narrow range of pH which is somewhat on the acid side. The hardening action is destroyed if the emulsion is subsequently made alkaline. The alum also binds other substances to the gelatin molecules. This effect is described as being similar to the mordanting used to make dyes fast. At neutral pH the mordanting action no longer takes place but most of the hardening action is still effective. If the gelatin is made more alkaline, for instance by treating it in a 2% solution of Sodium carbonate or Sodium Metaborate (Kodalk) both the mordanting action and the hardening are destroyed. Hardeners are used in the fixing bath to prevent undue swelling of the emulsion in both fixing bath and subsequent washing. The gelatin is quite vulnerable to scratching and gouging when swollen. Newer films have emulsions which are thoroughly hardened in manufacture and probably do not need the further hardening of the fixing bath but some still do. The effect of these two binding forces on the thiosulfate ions and on the fixer reaction products (silver and thiosulfate complexes) is to extend washing times by perhaps three times. The effect of both binding actions can be eliminated if: 1, the gelatin is never made acid; 2, if it is not treated with alum hardener and left in an acid condition. A neutral or somewhat alkaline fixing bath accomplishes the first purpose and, indirectly, the second because an alum, or other metallic hardener, will not work in an alkaline environment. What is the disadvantage of a neutral or alkaline fixing bath? Mainly that any carried over developer remains active until either washed out or exhausted or enough halide is dissolved to prent further development. Secondly, an acid stop bath can not be used and in any case any developer in the emulsion would be reactivated in an alkaline fixer so it would do no good. If the fixing bath contains sulfite, which it must to preserve the thiosulfate, the developer will not produce stains due to oxidation products but it may make a difference in the final amount of development of the negatives. Usually in non-acid development systems, like some color films, an intermediate wash is used between development and fixation which is sufficient to wash out the bulk of the developer. The development time and this rinse time are calculated to result in the proper amount of development. This same thing can be done in black and white of course. Non acid processing is used for some color films becaue the dyes which make up the image are bleached or otherwise changed by the acid. What are the advantages of acidified fixer? First, development can be stopped at a definite point by using an acid stop bath and any carried over developer will not be reactivated in the fixing bath. However, the main reason for using acid fixers is to make possible the use of metallic hardening agents. Hardening was once absolutely necessary but has not been for some decades. Now, the saving grace is that the advantages of an alkaline or neutral fixer can be obtained even when using an acid, hardening, fixing bath, by the use of a correctly compounded Sodium sulfite wash aid. Kodak Hypo Clearing Agent is such a wash aid, and is the only one on the market AFAIK, which is compounded correctly to get the full advantage of adjustment of the emulsion to the critical pH where it is above the isoelectric point and above the point where alum hardener acts as a mordant but still at a pH where hardening is preserved. This is done by buffering the Sulfite to neutral pH with bisulfite. However, most of the ability of a sulfite wash aid to accelerate washing is due to a different mechanism, namely an ion exchange function of the sulfite itself. Sulfite tends to actively displace thiosulfate and silver complex ions from the emulsion. The sulfite ions are left in their places but are much more easily washed out. The use of a buffered Sulfite wash aid on film reduces the wash time by about a factor of six over that when a hardening acid fixer is used, and about three times the wash time of a non hardening fixer. Becuse of the ion exchange property wash time is even less than when a non-hardening neutral or alkaline fixer is used, perhaps by half. This ion exchange effect also takes place in the fibers of uncoated paper support (non RC printing paper) as well as in the emulsion. While the paper support does not wash out by a strictly diffusion process, as does the emulsion, the rate at which thiosulfate bound up in the fibers leaves during washing is still very considerably accelerated and wash times shortened to about one third of untreated prints. Buffering to neutral has two advantages over using a simple sulfite solution: it preserves hardening where that is desired; it places the gelatin close enough to its isoelectric point to minimise swelling thus resulting in the shortest diffusion path for the various ions which is its desired to wash out. Sulfite wash aid was developed from research into sea water washing. It has been known for over a century that sea water washes out film and paper considerably. However, the reason for this was not known until research into it was carried out during and after WW-2. Sea water washing was much used in practice during the war in locations where fresh water was at a premium such as on board ships at sea. Sea water washing requies a final rinse in fresh water to wash out the halides and other substances in the sea water which other wise will cause very rapid degration of the image. But, even with this rinse, there is a very consdierable saving in fresh water. Kodak Research Labs discovered that the salt most similar to sea water in accelerating washing was Sodium sulfite. Other sulfite salts work but not as well. some othe salts have accelerating effects but are well below sulfite in effectiveness. Kodak Labs also determined that the pH should be neutral, for the reasons mentioned. In addition to the Sulfite and bisulfite KHCA also contains two sequestering agents, EDTA Tetra sodium salt, and Sodium citrate, which bind up carbonates and prevent them from being deposited on the surface of the emulsion. This is mainly necessary when there is no rinse between an hardening fixing bath and the wash aid or when the wash aid is re-used. Sulfite wash aid also makes some otherwise insoluble fixer reaction products, or those tightly bound to the image silver, soluble. The effect of this is to extend fixer capacity because these products are left by partially exhausted fixing baths. Nonetheless, for good premanence fresh fixer should be used or a two bath fixer should be used. The point of all this is that fixer does not work any better when alkaline. The effectiveness of thoiosulfate (either sodium or ammonium) is not affected by the pH of the solution: it works equally well in acid, neutral, or alkaline solution. The only justification for a neutral fixer in B&W phtography might be the preservation of the stain image when using a Pyro developer, but I am not convinced that what people are seeing is not an increase in the overall stain (fog level) when doing this. The imagewise stain left by Pyro is NOT a dye but rather a quite tough pigment related to humic acid. This stain image, BTW, is probably more permanent than the silver image it accompanies. I think I'm the one that got Richard started on this discourse, and I'm very grateful that he has taken the time to give such a clear and knowledgeable explanation of some fairly complex (to us English-major types trying to be "bathroom chemists") chemical reactions. Very helpful! One follow-up, Richard: I've been using Heico's "Permawash" for years as a washing aid. How does it compare with Kodak's Hypo Clearing Agent? Larry |
#10
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Tom Phillips wrote
Some claim to use alkaline fix to shorten wash time and conserve water. Never having used and tested it I don't know if this holds true or not. The ph of ALL off-the-shelf fixers is below seven. The ph of ALL off-the-shelf stop baths is below seven; the shelfs of the usuall photographic supply houses. If you found that the claim is true and wished to purchase an alkaline fix where would you turn? Dan |
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