[pure-silver] Re: HP5+ in 120 different from in 35mm?

At 02:04 PM 3/27/2008, you wrote:
I just noticed something weird. I processed three rolls of 120 format HP5+ today, and two rolls of 35mm HP5+, at the same time, using the same stop and fixer, in different tanks. It is drying now in the cabinet. The 120 film base clears to an almost transparent color, but the 35mm base seems much denser, a kind of gray blue. Why is this? 
Is it anything to worry about?

--shannon
This is quite normal. Most 35mm B&W film has a pigment in the support. The purpose is to prevent conduction of light, or light-piping, lengthwise in the film to prevent fogging when one end of the film is exposed to light as is the case when loading a camera. This base density makes no difference other than increasing printing time a little. The base pigment also helps prevent halation although most 35mm films also have a back coating for this. While the color in a back coating is decolorized in processing the pigments in the support can not be removed or decolorized so are permanent. A few B&W films have an anti-halation layer coated under the emulsion. This serves both to prevent halation and fogging from light-piping. This method is almost universal in color films. 



--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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