If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
"Geoffrey S. Mendelson" wrote in message ... In article , The Wogster wrote: I never used a stop bath with film, but 3 20 second water soaks, and then used the fixer 1 shot. Never had a problem. The use of a stop bath is really not needed for film, in fact there have been "monobath" (combined developer/fixer) products on the market and Edwal used to include instructions on how to use their developers as monobaths. The main reason to use one is to force development to end at a specific time so that the results are the same, but using the same rinse procedure will each time do the same thing (with slightly different results). It's also to keep the alkeline developer from mixing with the acid fixer. The acid in the fixer acts as an emulsion hardner. Some fixers include it, some include it as an option (remember the two bottle kodak rapid fixer with hardner?) and some don't have it at all. Geoff. -- Geoffrey S. Mendelson, Jerusalem Israel IL Voice: 972-544-608-069 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838 Its not the acid in the fixing bath that does the hardening. Common fixing baths use Potassium aluminum sulfate, also known as White Alum, or just Alum. The alum hardens the gelatin but works only over a fairly narrow range of pH. The hardening remains at neutral pH but is destroyed at much on the alkaline side of neutral. There are other hardeners, mostly organic compounds, which are effective hardeners in alkaline solution. These are common in color processing. Because the acid in an acid fixing bath reacts with the thiosulfate and eventually decomposes it some means must be provided to protect the thiosulfate. This is usually sodium sulfite. The large amount of sulfite needed also tends to prevent stains from the reaction products of carried over developer. Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. This tends to keep the pH of the bath in the right range for effective hardening despite carried over developer or carried over stop bath. This type of bath also tends to have less problem from sludging of the hardener when the pH is off the right value. It should be noted that the ability of thiosulfate to fix is independant of pH. The odor from fixing baths is due to some decomposition of the thiosufate by the acid. Making the bath less acid will reduce the odor. Neutral fixing baths, essentially just thiosulfate and sulfite, are very low odor. Citric acid or sodium bisulfite or sodium metabisulfite can be used for odorless stop baths. Citric acid is not ideal for use with fixers using alum hardeners because it is a sequestering agent for aluminum and will cause reduction of hardening and may also cause sludging. Many modern films do not require hardening so do not need fixers which are acid. I seen no advantage whatever in making a fixing bath alkaline but making neutral fixer is fine. Also, the swelling of the emulsion will be less in a neutral bath than in either an acid or alkaline bath. There is an advantage in washing if the emulsion is neutral when it it is washed. If an acid hardening fixer is used a buffered sulfite wash aid, like Kodak Hypo Clearing Agent, will adjust the pH to neutral and also eliminate the binding effect of the alum on thiosulfate and fixer reaction products. Wash times when the emulsion is treated in such a bath are the same regardless of the type of fixing bath used. In addition the sulfite acts as an ion exchanger for thiosulfate so the wash is very much accelerated over what one would have from a simple neutralizing bath without sulfite. I still think acid stop baths prevent more problems than they cause but certainly a plain water rinse works if it actually washes out the bulk of the developer. BTW, someone mentioned monobath processing. Much of the research on this was done by Grant Haist. He wrote a small book called _The Monobath Manual_ (very hard to obtain now) and also covers monobaths in his _Modern Photographic Processing_. Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. -- --- Richard Knoppow Los Angeles, CA, USA |
#12
|
|||
|
|||
On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email |
#13
|
|||
|
|||
On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email |
#14
|
|||
|
|||
John wrote: On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. yeah I think he should consider adding a regular joke line to his sig Who knew? snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Unless one _is_ alkaline I'd use a stop. Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email |
#15
|
|||
|
|||
John wrote: On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. yeah I think he should consider adding a regular joke line to his sig Who knew? snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Unless one _is_ alkaline I'd use a stop. Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email |
#16
|
|||
|
|||
"Richard Knoppow" wrote
There are other hardeners, mostly organic compounds, which are effective hardeners in alkaline solution. Now days the integrity of incorporated hardeners is more of a concern. Most B&W processing is done without hardeners added to the chemistry. Developers can be very alkaline. Have you any idea just how alkaline they can be and not degrade the film's or paper's incorporated hardener? I've a notion that most films and papers are pre-process hardened as fully as any in-process hardener will do, even more so. Is that notion correct? Perhaps pre-process hardening is less than if there were none and the hardening left to an in-process hardener. Maybe a combination of the two would result in the most hardened emulsion possible. What do you think? Dan |
#17
|
|||
|
|||
John wrote in message . ..
On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email Of course, I meant fixing bath although buffered stop baths are also possible and will have a longer life than a plain acetic or citric acid bath. Grant Haist goes quite deeply into monobaths, evidently this was a subject of his research work at Kodak. Many monobaths do use sodium hydroxide as the accelerator, the reason is simple: the developer must compete with the fixer. Development must be completed before enough of he halide is removed to destroy the image. Monobaths must also contain a hardener. Haist has formulas with Glutaraldehyde but also lists a number of oganic hardeners suitable for use in highly alkaline baths. In both of his books Haist shows formulas optimized for Tri-X (roll film) and Verichrome Pan, I think a couple of others but I am away from my books at the moment. At least a couple of these formulas include Phenidone as a primary developing agent. I should point out that the hardener in fixing baths was intended to compensate for the swelling caused by both the alkaline developer and the acid fixer. Auxilliary hardeners are less necessary where the pH of the solutions does not vary from neutral by much. Eliminating the stop bath is attractive but there is still the problem of stopping the development quickly and keeping developer from carrying over to a neutral or alkaline fixing bath where it can continue development. A long rinse in running water seems to be the solution. This is the method used in alkaline color processing. Rinses are typically 1 to 3 minutes. Where highly alkaline developers are used, such as lithographic developers, it is common practice to use an anti-swelling stop bath. Typically this has about 15 grams/liter of Sodium sulfate in it (sulfate not sulfite). Sulfate is also used in tropical developers to reduce emulsion swelling and slow the rate of development. Since many B&W films, for instance T-Max, are now made to withstand 100F processing such measures are not necessary for them. However, films like Tri-X are still relatively sensitive to emulsion swelling. It was also common in tropical processing and lith processing to use a chrome-alum stop bath. Chrome alum is acid and is a very effective hardener. However, it must operate at very low pH (around 2.0) so is difficult to incorporate into fixing baths although there are chrome alum fixing baths. Its use is probably not necessary for any film these days. With all the talk about alkaline processing and eliminating stop baths it seems to have gotten lost that this procedure has been used with completely satisfactory results for many decades. The proper use of an acid stop bath stops development quickly and prevents carryover of active developer into the fixing bath. It also prevents the possible generation of developer stain where it is allowed to continue in a bath without sulfite. It also seems to me than in reading the reasons for not using acid stop baths I am really seeing complaints of problems from bad practice. Even complaints about odor can be solved by using acids other than Acetic acid. Pin holes are extremely unlikely to be caused by any conventional packaged developer or fixer. For one thing modern emulsions are not very vulnerable to it and very few current film developers use carbonate, the villan in outgassing. A pinhole is an actual disruption of the emulsion. I suspect that very often what people are seeing are small clear spots caused by dust on the negative. Pin holes CAN occur because of coating problems. These exist in the emulsion from the manufacturer. A very great deal of research and technical development has gone into making very consistent coatings. This is very well established technology but even the best manufacturers may have problems especially in these days of low sales and cost cutting. Personally, I suspect the whole movement to use alkaline processing is a sort of belief in black magic. Well, folks, there just isn't any black magic in photographic chemistry anymore. Even emulsion making, once one of the most closely guarded proprietary secrets in any industry, are now public record and anyone who is willing to do some research, AND has a decent understanding of organic and colloid chemistry, can find out how its done. Now, watch the flames come:-) Richard Knoppow Los Angeles, CA, USA |
#18
|
|||
|
|||
John wrote in message . ..
On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow" wrote: Richard, Great post as usual. snip Because modern stop baths were devised to work with or without a stop bath they are heavily buffered by using a combination of Acetic acid and Boric acid. Perhaps you meant "fixing baths" ? Monobaths are not simply a mixture of developer and fixer. They must be very carefully formulated and matched to a specific emulsion. They have some very interesting properties, not least of which is very considerable immunity to temperature and time variations. Haist shows some examples suggesting the possible image quality is very high. For some reason monobaths have never become popular except for some special rapid access uses. I think it's just as you indicated that they need to be formulated for specific films and I would add that those formulas were used one-shot and probably had limited stability due to the high alkalinity. The formulas that I'm familiar with use hydroxide as an accelerator. Perhaps there are other agents used ? Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email Of course, I meant fixing bath although buffered stop baths are also possible and will have a longer life than a plain acetic or citric acid bath. Grant Haist goes quite deeply into monobaths, evidently this was a subject of his research work at Kodak. Many monobaths do use sodium hydroxide as the accelerator, the reason is simple: the developer must compete with the fixer. Development must be completed before enough of he halide is removed to destroy the image. Monobaths must also contain a hardener. Haist has formulas with Glutaraldehyde but also lists a number of oganic hardeners suitable for use in highly alkaline baths. In both of his books Haist shows formulas optimized for Tri-X (roll film) and Verichrome Pan, I think a couple of others but I am away from my books at the moment. At least a couple of these formulas include Phenidone as a primary developing agent. I should point out that the hardener in fixing baths was intended to compensate for the swelling caused by both the alkaline developer and the acid fixer. Auxilliary hardeners are less necessary where the pH of the solutions does not vary from neutral by much. Eliminating the stop bath is attractive but there is still the problem of stopping the development quickly and keeping developer from carrying over to a neutral or alkaline fixing bath where it can continue development. A long rinse in running water seems to be the solution. This is the method used in alkaline color processing. Rinses are typically 1 to 3 minutes. Where highly alkaline developers are used, such as lithographic developers, it is common practice to use an anti-swelling stop bath. Typically this has about 15 grams/liter of Sodium sulfate in it (sulfate not sulfite). Sulfate is also used in tropical developers to reduce emulsion swelling and slow the rate of development. Since many B&W films, for instance T-Max, are now made to withstand 100F processing such measures are not necessary for them. However, films like Tri-X are still relatively sensitive to emulsion swelling. It was also common in tropical processing and lith processing to use a chrome-alum stop bath. Chrome alum is acid and is a very effective hardener. However, it must operate at very low pH (around 2.0) so is difficult to incorporate into fixing baths although there are chrome alum fixing baths. Its use is probably not necessary for any film these days. With all the talk about alkaline processing and eliminating stop baths it seems to have gotten lost that this procedure has been used with completely satisfactory results for many decades. The proper use of an acid stop bath stops development quickly and prevents carryover of active developer into the fixing bath. It also prevents the possible generation of developer stain where it is allowed to continue in a bath without sulfite. It also seems to me than in reading the reasons for not using acid stop baths I am really seeing complaints of problems from bad practice. Even complaints about odor can be solved by using acids other than Acetic acid. Pin holes are extremely unlikely to be caused by any conventional packaged developer or fixer. For one thing modern emulsions are not very vulnerable to it and very few current film developers use carbonate, the villan in outgassing. A pinhole is an actual disruption of the emulsion. I suspect that very often what people are seeing are small clear spots caused by dust on the negative. Pin holes CAN occur because of coating problems. These exist in the emulsion from the manufacturer. A very great deal of research and technical development has gone into making very consistent coatings. This is very well established technology but even the best manufacturers may have problems especially in these days of low sales and cost cutting. Personally, I suspect the whole movement to use alkaline processing is a sort of belief in black magic. Well, folks, there just isn't any black magic in photographic chemistry anymore. Even emulsion making, once one of the most closely guarded proprietary secrets in any industry, are now public record and anyone who is willing to do some research, AND has a decent understanding of organic and colloid chemistry, can find out how its done. Now, watch the flames come:-) Richard Knoppow Los Angeles, CA, USA |
#20
|
|||
|
|||
On 14 Nov 2004 04:43:30 -0800, (Richard
Knoppow) wrote: Well, folks, there just isn't any black magic in photographic chemistry anymore. Doggone it ! Ansel beat me to all that Black Magic developer !! Regards, John S. Douglas, Photographer - http://www.puresilver.org Please remove the "_" when replying via email |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Focal plane vs. leaf shutters in MF SLRs | KM | Medium Format Photography Equipment | 724 | December 7th 04 09:58 AM |
Advice for camera bag, film developing and film choice | JZ | 35mm Photo Equipment | 4 | August 24th 04 08:56 PM |
Kodak on Variable Film Development: NO! | Michael Scarpitti | In The Darkroom | 276 | August 12th 04 10:42 PM |
Is it Copal or copal? Then what is it? | Nick Zentena | Large Format Photography Equipment | 14 | July 27th 04 03:31 AM |
below $1000 film vs digital | Mike Henley | Medium Format Photography Equipment | 182 | June 25th 04 03:37 AM |