Usenet Newsgroups Re: Pyro Developers Question. From: ian@lostlabours.co.uk (IanG) On Aug 13, 3:27 pm, Lew <lew1...@gmail.com> wrote: Isn't there also the claim that, as development & tanning progress in highlight areas, the emulsion physically compresses (as a result of the tanning) thereby holding less developer? ie there is even more moderation of highlight densities than there is via the mechanism of developer exhaustion alone. I haven't tested this extensively, but my limited experience leads me to believe that, on a very sunny day, with the sun overhead, plus areas of deep shadow, using iso 200 - 400 films, I did obtain easy to print negatives with plenty of highlight detail. Pyrocatechin (and Pyrogallol) work by acting on the surface of the emulsion tanning & hardening the emulsion as the developers is used and oxidises, particularly in the highlights. It's the basis of the Pyrocatechin surface developers used to control high contrast lighting as advocated by LP Clerc and Hans Windisch etc. So yes you are correct. The same effect is used in some Lith/Graphic arts  developers, German formulae often used Pyrocatechin in place of Hyrdroquinone, the two are to some extent interchangeable. Kodak also used Pyrocatechin instead of Hydroquinone in HC110 for a while. Ian Subject  Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Jobo atl3  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Pyro Developers Question.  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Jobo atl3  Re: Pyro Developers Question.  Re: Pyro Developers Question.