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  1. #11

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    It is not that the gelatin doesn't swell. Film manufacturers aim about 300% swelling of gelatin used in emulsion layer because this range is optimum in terms of saving silver and obtain high density. This is less swelling than 1950 stuff, but gelatin still swells 300%.

    When film is transferred to bath B, diffusion of both directions occur, as in Donnan membrane mechanism. The effective development time in "mixing in gelatin" mechanism is very short. In order to achive effective development in that short time span, development centers must grow to a sufficient size while the film is in bath A. One could say that the induction process must happen in bath A alone.

    I personally do not recommend propylene glycol. When a LOT of it is present in developer solution, it may be effective in prolonging the stock's shelf life, but if you use it in split stock solution, it is very easy to infringe one of the Kodak patents. Another problem with propylene glycol (and actually many alcohols and glycols) is that when the stock solution is diluted, so that the glycol concentration becomes low enough, the presence of PG can actually accelerate aerial oxidation of ascorbate compared to when there is no PG! I did tests on this with an array of solutions stored in bottles with aerobic stoppers for 2 months, at that point developer composition and chemical activity were measured.

    Triethylene glycol is slightly better than propylene glycol in this regard, although TEG also accelerates ascorbate loss. I think that PG is more effective in oxidizing ascorbate because two alcohols are vicinally positioned to increase binding to metal impurities. If so, compounds like 2,4-pentanedione (acac) would be more effective in killing ascorbate. Anyway, beware of nonaquaous solvents.

    I'm trying to do the opposite of what's described above by making some derivatives of those compounds that posses desirable properties. Let's see how it goes...

  2. #12

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    Quote Originally Posted by Ryuji
    Using bubbling as an indicator is very unreliable. You should at least get fine grain pH test strips (they come in narrow window of pH range so you need a few different sets). You also might want to get a few pH indicator dyes for different pH ranges. For usual darkroom work, these are often sufficient.
    Donald - I suggest something like the Whatman multistrip indicating papers http://www.whatman.com/products/?pageID=7.29.24
    I use the CF paper which measures from 0-14 with about 1 pH resolution, for making quickie pH measurements. You can get papers that are in narrower ranges too if you have a range you want to focus on.

    Of course, these aren't as high-tech as an actual meter, but as Ryuji points out on his web site - there are a lot of things to consider with the meter route to make good, reliable pH measurements. And for what you are doing, I think the strips will be quite helpful.

    Kirk - www.keyesphoto.com

  3. #13
    Donald Qualls's Avatar
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    Kirk, good suggestion, but I have no budget whatever here -- I'm trying to learn something and possibly produce something with what I have on hand. And since there's an expert opinion that nothing I can possibly do will produce a workable divided developer with ascorbate, I'll just go away.
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  4. #14

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    To cite a early 20th Century comment: Insects can't fly (a simplified translation of Magnan's statement in his 1934 book).

    In 1934, French entomologist Antoine Magnan included the following passage in the introduction to his book Le Vol des Insectes:


    Tou d'abord poussé par ce qui fait en aviation, j'ai appliqué aux insectes les lois de la résistance de l'air, et je suis arrivé avec M. SAINTE-LAGUE a cette conclusion que leur vol est impossible.


    Magnan's reference is to a calculation by his assistant André Saint-Lagué, who was apparently an engineer.


    This statement eventually morphed into: "Like the bumblebee, they said it could never fly."

    http://www.sciencenews.org/articles/...1/mathtrek.asp
    Tom Hoskinson
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    Everything is analog - even digital :D

  5. #15
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    Quote Originally Posted by Ryuji
    It is not that the gelatin doesn't swell. Film manufacturers aim about 300% swelling of gelatin used in emulsion layer because this range is optimum in terms of saving silver and obtain high density. This is less swelling than 1950 stuff, but gelatin still swells 300%.

    When film is transferred to bath B, diffusion of both directions occur, as in Donnan membrane mechanism. The effective development time in "mixing in gelatin" mechanism is very short. In order to achive effective development in that short time span, development centers must grow to a sufficient size while the film is in bath A. One could say that the induction process must happen in bath A alone.

    I personally do not recommend propylene glycol. When a LOT of it is present in developer solution, it may be effective in prolonging the stock's shelf life, but if you use it in split stock solution, it is very easy to infringe one of the Kodak patents. Another problem with propylene glycol (and actually many alcohols and glycols) is that when the stock solution is diluted, so that the glycol concentration becomes low enough, the presence of PG can actually accelerate aerial oxidation of ascorbate compared to when there is no PG! I did tests on this with an array of solutions stored in bottles with aerobic stoppers for 2 months, at that point developer composition and chemical activity were measured.

    Triethylene glycol is slightly better than propylene glycol in this regard, although TEG also accelerates ascorbate loss. I think that PG is more effective in oxidizing ascorbate because two alcohols are vicinally positioned to increase binding to metal impurities. If so, compounds like 2,4-pentanedione (acac) would be more effective in killing ascorbate. Anyway, beware of nonaquaous solvents.

    I'm trying to do the opposite of what's described above by making some derivatives of those compounds that posses desirable properties. Let's see how it goes...
    Without contradicting what you have done, I don't think it is what I have done. As you said, the use of glycols preserves the stock solution. A simple solution of ascorbic acid and phenidone is useful. The working solution needs not last any longer than the developing time, and I have not seen it fail. When it comes to patents, it is difficult to patent anything that would likely be designed by a competent engineer. Perhaps you can inform me who was first to use a glycol as a solvent for developing agents, and if the first one tried to patent that process. It is quite common for engineers to search for useful solvents among many possible useful ones. The Patent Office will often grant a patent, but will not defend it for one.

    Come to think of it, I'm not sure anyone ever tried to patent water as a solvent for photographic chemicals.
    Gadget Gainer

  6. #16

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    Patrick, patent is a conceptually simple system but in order to understand how it works, you should spend some time studying the system. Much of what you said are irrelevant to the criteria of patentability.

    A lot of things can be patented. It mostly depends on how you write claims and support claims in the specifications. There are lots of VERY funny examples, but check out US Patents 5443036 and 5851117 for example.

    Patent examiners have a set of legal standards to decide whether the invention is patentable as described in the application. Good patents have a set of very strong, broad claims (independent claims) and a lot of specific claims derived from the independent claims (dependent claims). Good claims are ones that good implementations would have to infringe at least one of them. But if the invention is weak (not novel enough, not useful, or too obvious to those skilled in the art) patent examiner will negotiate to strip down the claims or make claims narrower. Consequently, if the invention is not very strong, it may be patented but the claims are virtually useless and many people could implement the idea without infringing any of them.

    On the other hand, details disclosed in the specification must support the invention and they also have to disclose the best mode of implementation known to the inventor. Regardless of how useful or useless the claims are, what's written in the specification can be used as a reason to reject future applications of inventions using that knowledge as a key element. Thus patents have two major aspects of defining your legal rights related to your invention. If you want to know more, you should consult a patent attorney or consultant.

    Use of water as a solvent for developer is clearly not patentable alone, but if there are enough specifics to make the case special, it may be patentable. But this is true of many things.

  7. #17

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    Quote Originally Posted by Donald Qualls
    Kirk, good suggestion, but I have no budget whatever here -- I'm trying to learn something and possibly produce something with what I have on hand. And since there's an expert opinion that nothing I can possibly do will produce a workable divided developer with ascorbate, I'll just go away.
    I didn't mean to discourage you or anyone, but I merely pointed out that the problem you were dealing with is not a trivial one for amateurs.

    Now the pH problem, since Kirk continued on that issue.
    In my experience of phenidone-ascorbate developers, in very general terms, the developer pH difference of 0.2 is photographically very significant, even to a casual observer without formal sensitometry, especially if the developer pH is below 9.3 or so. I try to adjust pH to plus/minus 0.05 for film developers.

    A good developer design would have to be that, when a batch of developer is mixed with reasonable care, the solution pH is well within the target pH window, and the developer performance is robust against small errors in chemical weighing, film difference, exposure difference, etc. I understand that most people on apug are darkroom hobbists who make the chemicals for themselves, without worrying too much about reproducibility and robustness, but these are definitely important practical aspects and pH is one of the most fundamental values to be controlled.

  8. #18
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    The use of polyoxy, polyhydroxy and polyamino addenda in developers (read poly ethylene and propylene glycols, poly vinyl alcohols, and poly vinyl pyrrolidones) along with TEA and a host of other amines have been known since the 50s.

    Many many patents have issued on these addenda, and many overlap with couter claims and claims within claims.

    In some cases, you might find yourself infringing a whole set of patents with one of these compounds at one concentration, and end up theoretically owing redress to several companies at one time. Then the courts would have to figure out who got what if anything.

    Expired patents are of no concern for any infringement purposes. They are free to use in any way.

    PE

  9. #19

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    Quote Originally Posted by Ryuji
    Another problem with propylene glycol (and actually many alcohols and glycols) is that when the stock solution is diluted, so that the glycol concentration becomes low enough, the presence of PG can actually accelerate aerial oxidation of ascorbate compared to when there is no PG!
    Have you tried PEG - polyethylene glycol - about 200 MW? (I happen to have a bout 500 ml sitting on the shelf looking for a good use.)

    Any advantage to using larger glycol molecules?

  10. #20

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    Two suggestions re the original question.Simple may not be optimal but may be good enough to get started.

    1-Afairly concentrated solution of vit C and phenidone may get enough ascorbate into the emulsion to cause development in sodium carbonate.

    2-A solution of sodium ascorbate as part A may be more stable but it is harder to get I believe.

    IIRC the phenidone should be about 1/40 the ascorbate by weight.

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