Photo Engineer
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I have posted some of my reasoning here:
(there was a url link here which no longer exists)
In my posts, I state some of the reasons why I want a long life developer. I first began the quest for this back in 1965 for B&W and color developers, and the result was a testing methodology for both seasoning and keeping and a US patent (3,615,503 Edens, Mowrey) for the old C-22 developer. It was also applied to the EP3 developer.
Well, here is the reasoning and it applies to both color and B&W.
A developer ages or seasons for virtually the same reasons. The pH changes (down), the developing agent chages (down), the antioxidant(s) change (down) and the halide content changes (up but only with seasoning). The big difference is that an aging developer in an open container also changes by evaporation if the time span is long enough. In addition, this evaporation varies as a function of surface to volume ratio. For example, 1 liter in an 11x14 tray evaporates and changes faster than the same amount in an 8x10 tray, and this changes more than the same amount in a 5x7 tray.
The result of the above is this; you can meter the capacity and lifetime of a developer simply by placing it in an open tray and running a print through it every day at the same time and temperature and with the same exposure. The change in the gray scale produced is a measure of either capacity or resistance to oxidation or a combination of both. The test can be as long or as short as you wish. Usually, one week will reveal total capacity or life or a combination of both. Sometimes only a day or so is needed.
At the end of the test, you then make an additional print but develop by inspection in an effort to regain the original sensitometry by increasing development time. This tells you if the developer is truly dying, or is just losing activity and these are two big differences, believe me!
In addition, you measure the pH of the developer at the start and at the end of the test. This gives you a measure of the effect of carbon dioxide and oxidation on this critical feature.
Now, here are some findings. First, the size of the tray only changes the speed at which a developer changes, it does not change the rank ordering of developers. Second, evaporation increases buffer capacity somewhat, but pH can still go down and in most cases, pH is more important than buffer capacity at normal working dilutions. Third, sulfite or other antioxidants are used up and some developers may turn color, some may stain, and some may turn into a sludge or cause a sludge to settle out. This may or may not be harmful.
The ideal goal of course is that if I'm going to make 25 prints that I want to be identical, I want a high capacity, stable developer. I don't want to start the job, go to lunch and return to the darkroom only to start over again or adjust printing time or contrast or development time.
As stated elsewhere, some developers appear the same on superficial examination, but show slight changes in toe or upper shoulder that can alter a print. This is not good.
Now you may say - use more developer, change developer more often and etc etc. This is all true, but finding out how much to use or when to change may be part of the problem. For example, some developers change regardless of how much you use, simply because they are poorly 'buffered' in all ingredients. Therefore, one developer may allow 20 8x10 sheets / liter, and another may begin showing changes after only 5 or 10 sheets. This also varies with respect to scene. A dark scene changes the developer more rapidly than a light one. At Kodak, we used the average of 30% of the silver being developed in an average scene, but this is averaged over thousands of prints. So, if you are doing a snow scene as opposed to a dark evening scene, things work out differently over the same 10 - 20 prints in a given developer. I've run into this, espeically with silver rich papers, or unwashed emulsions which I'm testing. It is also important with papers that contain developing agents as opposed to those which do not.
So, you see the complexity of judging how much to use and how long. I want to remove this problem by having a high capacity, long lasting developer regardless of paper or scene.
I have a list of developers to test, and I'm only part way through the list, so I will not be publishing any data yet. The results so far are rather surprising, to say the least. Stay tuned.
PE
(there was a url link here which no longer exists)
In my posts, I state some of the reasons why I want a long life developer. I first began the quest for this back in 1965 for B&W and color developers, and the result was a testing methodology for both seasoning and keeping and a US patent (3,615,503 Edens, Mowrey) for the old C-22 developer. It was also applied to the EP3 developer.
Well, here is the reasoning and it applies to both color and B&W.
A developer ages or seasons for virtually the same reasons. The pH changes (down), the developing agent chages (down), the antioxidant(s) change (down) and the halide content changes (up but only with seasoning). The big difference is that an aging developer in an open container also changes by evaporation if the time span is long enough. In addition, this evaporation varies as a function of surface to volume ratio. For example, 1 liter in an 11x14 tray evaporates and changes faster than the same amount in an 8x10 tray, and this changes more than the same amount in a 5x7 tray.
The result of the above is this; you can meter the capacity and lifetime of a developer simply by placing it in an open tray and running a print through it every day at the same time and temperature and with the same exposure. The change in the gray scale produced is a measure of either capacity or resistance to oxidation or a combination of both. The test can be as long or as short as you wish. Usually, one week will reveal total capacity or life or a combination of both. Sometimes only a day or so is needed.
At the end of the test, you then make an additional print but develop by inspection in an effort to regain the original sensitometry by increasing development time. This tells you if the developer is truly dying, or is just losing activity and these are two big differences, believe me!
In addition, you measure the pH of the developer at the start and at the end of the test. This gives you a measure of the effect of carbon dioxide and oxidation on this critical feature.
Now, here are some findings. First, the size of the tray only changes the speed at which a developer changes, it does not change the rank ordering of developers. Second, evaporation increases buffer capacity somewhat, but pH can still go down and in most cases, pH is more important than buffer capacity at normal working dilutions. Third, sulfite or other antioxidants are used up and some developers may turn color, some may stain, and some may turn into a sludge or cause a sludge to settle out. This may or may not be harmful.
The ideal goal of course is that if I'm going to make 25 prints that I want to be identical, I want a high capacity, stable developer. I don't want to start the job, go to lunch and return to the darkroom only to start over again or adjust printing time or contrast or development time.
As stated elsewhere, some developers appear the same on superficial examination, but show slight changes in toe or upper shoulder that can alter a print. This is not good.
Now you may say - use more developer, change developer more often and etc etc. This is all true, but finding out how much to use or when to change may be part of the problem. For example, some developers change regardless of how much you use, simply because they are poorly 'buffered' in all ingredients. Therefore, one developer may allow 20 8x10 sheets / liter, and another may begin showing changes after only 5 or 10 sheets. This also varies with respect to scene. A dark scene changes the developer more rapidly than a light one. At Kodak, we used the average of 30% of the silver being developed in an average scene, but this is averaged over thousands of prints. So, if you are doing a snow scene as opposed to a dark evening scene, things work out differently over the same 10 - 20 prints in a given developer. I've run into this, espeically with silver rich papers, or unwashed emulsions which I'm testing. It is also important with papers that contain developing agents as opposed to those which do not.
So, you see the complexity of judging how much to use and how long. I want to remove this problem by having a high capacity, long lasting developer regardless of paper or scene.
I have a list of developers to test, and I'm only part way through the list, so I will not be publishing any data yet. The results so far are rather surprising, to say the least. Stay tuned.
PE
