From: "John Black" <jblack@xxxxxxxxx> Subject: [pure-silver] Re: Pyro in a Jobo Processor Date: Mon, 21 Mar 2005 13:55:27 -0500 > That reminds me. I have some trouble with 35mm film "cupping" or "bowing" > rather badly after drying and this must be due to excessive shrinkage of the > emulsion relative to the backing or any other layers on the reverse. Does > anyone have a remedy for this and would it benifit to cross-link or "harden" > the emulsion to prevent excessive shrinkage? I know hardening was used to > toughen up older, soft, thick emulsion films and mostly isn't needed now, > but could it help prevent shrinkage? I think that has more to do with the film base, whether cellulose triacetate or polyester, which is poly(ethylene telephthalate). It also depends on the plasticizer used in the emulsion. Modern emulsions incorporate nongelatin polymer macromolecules in part to achieve plasticizing effect, maybe in addition to large sugar alcohol molecules. In old emulsions small molecules like glycerol and other small polyols were used but these agents would only help plasticizing unprocessed materials, since they will be lost during processing due to their diffusibility in gelatin. > Agreed. My own tests show pH to be the most important issue affecting > graininess followed by temperature. Assuming proper developing time and > exposure. A&T and even Haist continue to speak of "grain clumping" though > in their literature. I wouldn't take A&T to the accuracy of every word they printed. The value of their work was to make some parts of the material more accessible to the average darkroom workers. > > Also, I think electrophoresis is done on crosslinked polyacrylamide or > > maybe some other polymer, which is quite different from gelatin. > > Maybe not so different as you might think. Until it was halted, I > understand resources at Kodak were being spent in pursuit of "artificial > gelatin" or a sythetic gel with the AgX binding properties of natural > gelatin and progress had been made. Remember, polyacylamide gel came about > as a substitute for highly purified agar. Polyacrylamide is/was used as a gelatin blend in commercial materials. I know Fuji has been and is still active in this area. I don't know if Kodak halted this research either. As far as I know no polymer blend is capable of displacing gelatin in photographic emulsion even today. The fraction of synthetic polymers as well as modified gelatin polymers has been increased, but still it's not large. There are some recent patents that use non-gelatin molecules like starch as the peptizing agent but clearly such an emulsion has to incorporate another binder (such as gelatin) later in the process, making the process very complicated. I doubt that kind of technique is used in current production. -- Ryuji Suzuki "Keep a good head and always carry a light camera." ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.