Response to Base fog

Some films use a denser base than others to prevent halation and light piping. The light striking the protruding leader of 35 mm film is "piped" along the film. A base density of 0.1 becomes a very high density very quickly along the film and is sufficient to prevent piping. Films with this low base density use other means of preventing halation. HP5+ will never be as clear as TMX for this reason. If you remove the emulsion from a piece of HP5+ by soaking it in Clorox you will see a density of about 0.3, 1 stop. This density can be printed through and has no effect on the density range of the negative or its graininess. It is no different than stopping down one stop. Chemical fog is all you have to worry about. Develop an unexposed piece of film, fix it and compare it with a piece cleared in Clorox. The difference shows the minimum chemical fog you will get in that developer. There is also the appearance of fog caused by flare in camera or enlarger. This fog does change the apparent characteristic curve of the film from what you would get in lab tests without flare, generally changing a short toe film to a long toe.

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