----- Original Message ----- From: Rob Studdert Subject: Re: Pre-Rinse in Development Land ?
> On 1 Jun 2002 at 11:39, William Robb wrote: > > > Here are my thoughts on film washing. > > It takes about 15 seconds for the emulsion to absorb whatever > > solution it is in, and displace whatever solution was already > > soaked into it. So, if the film is soaked for twice the solution > > absorbtion time, it will definitely have diluted the fixer as > > much as it is going to in each wash tank. > > If you are exceptionally paranoid, then go a minute per tank. > > Now for some math: > > I did some testing and discovered that a 135/36 or 120 roll of > > film absorbs about 20ml of solution on the reel. A steel tank > > holds about 250ml of solution per film. > > Your first wash bath of 30 seconds will leave about .08 ml of > > fixer behind. Your second 30 second wash will leave about .00032 > > ml of fixer behind, and a third wash will leave .00000128 ml of > > fixer as residue over the entire film. > > But is that what the wash does? I was lead to believe that the length of wash > time was determined in order to ensure that all the soluble salts were leached > from the gelatin? For film, all we have to do is ensure that the fixer is diluted to the point where it is effectively gone. There are no paper fibers to hold the sulpher salts. Washing film is very much like washing resin coated paper. The residual fixer washes out very easily. In a running water wash, the times have to be longer because the tank change over isn't as rapid as it is with fill and dump, and also the turbulence from a running water wash actually slows down the diffusion of chemistry from the emulsion into the bath. William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
