Hi: This what I think may be happening.
As film is developed the developer looses its activity. A film must be developed in a volume of developer with enough capacity to fully develop the film. As the film is developed the developer in immediate contact with the film looses its activity. This locally expired developer must be replaced with fresh developer that has not been "developed out". If there is a sufficient volume of developer there should be an adequate volume of fresh developer. Agitation provides the film with a consistent supply of fresh developer. Without agitation the developer adjacent to the film becomes exhausted, thus development stops or slows down considerably. More agitation provides the film with more fresh developer allowing it to develop more. At some point increasing the rate of agitiation provides a continuous supply of fresh developer. Increasing the rate of agitation beyond this point will not provide any more fresh developer, and should not have any effect on contrast. The point at which additional agitation does not affect development is likley unique for each film and developer combination. Most commmon way of adjusting contrast in by changing development time. pH of developer can change developer activity as well - but thats not commonly used. Gord On Mon, 6 Aug 2001, William Erickson wrote: > I've been using large format pinhole negatives to do alternative process > printing. I've been aware for some time of the extent to which I can > influence the contrast of a tray-processed TMAX negative by the amount of > agitation I provide. I understand that TriX is much less susceptible to > contrast control this way, but I've never tried it. I just tried some Ilford > HP5 5x7 negatives intended for cyanotypes and palladium printing, and found > much less contrast than I expected with what I thought was over-agitation. > Any thoughts? > > > _______________________________________________ > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/ > --------------------------------------------------------- Gordon J. Holtslander Dept. of Biology hol...@duke.usask.ca 112 Science Place http://duke.usask.ca/~holtsg University of Saskatchewan Tel (306) 966-4433 Saskatoon, Saskatchewan Fax (306) 966-4461 Canada S7N 5E2 ---------------------------------------------------------
