Archived posting to the Leica Users Group, 2005/11/23
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>From what I have read, a long time ago Kodak and other manufacturers had different gelatin and film bases that were not as cohesive as modern films and emulsions. The gelatin was softer, weaker and could tear more easily. Sometimes when the developing film went from a carbonate buffered developer into an acid stop bath, CO2 was formed by acid-base reaction from carbonate and the effervescence in the would tear gelatin specs off the film base, leaving a clear spot in the negative. This would be more likely to happen if the temperature was above 68?F (20?C) for the process solutions. Modern films have pre-hardened gelatin, so this is less likely to happen now, unless you are working in tropical temperature conditions. If you are making your own developer solutions, you can switch to a Borax or Borate buffering system, which will not effervesce. There may be commercial developers with Borax buffer, but I don't know of them. While there may be some developers that are acidic or continue to have some activity in acid, most are still carbonate buffered, and the pH change and developer dilution of putting film into a stop bath ensure a precise end to development, while water alone may allow more continued development. I usually use a 1.5% Citric acid stop bath. A 15% (or 30%) Citric acid stock solution seems to be quite stable, does appear to grow microbes, does not smell like acetic acid and is quickly diluted 1:9 from 15% (or 1:20 from 30%) for working stop bath. >At 04:05 PM 11/22/2005, Henning Wulff wrote: > >>The main problem is that pinholes can develop. >>If you do use any 'stop bath', dilute it a lot. >>... Richard <richard-lists@imagecraft.com> wrote >What exactly are pinholes? Actually holes in the negatives or the emulsion? > -- ______________________________________________________________________________ Steve Keirstead Research Assistant II, Biology Teaching Labs, Harvard Science Center, Room 409, 1 Oxford Street, Cambridge, Ma 02138. Work Phone: (617) 495-2683 , FAX: (617) 496-9105