[pure-silver] Re: Ilford washing film technique, and scientific research

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Fri, 17 Aug 2007 07:29:15 -0700


----- Original Message ----- From: <anclancy@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, August 17, 2007 4:55 AM
Subject: [pure-silver] Re: Ilford washing film technique, and scientific research



Several years ago when we had serious water conditions we switched to Ilford's method. This was after doing serious research with others who have used their method for more than 10 -15 years.

At this point and time the negatives are still holding up .

just my 2cents.

regards,
ann

The sequential bath method (to coin a name) has been around for many decades. Ilford's method differs from Kodak's in that it takes into account the inverse exponential rate of the diffusion of hypo from the emulsion. That is, the rate of diffusion is proportional to the ratio of hypo in one medium to the other. The more hypo there is in the emulsion and the less in the water the faster the hypo leaves. As washing progresses equilibrium is approached faster at the beginning than at the end. Ilford takes this into account by having a short interval at the beginning of the wash process and allowing each bath to become longer. Kodak uses uniform intervals. There is probably no difference in the amount of hypo left at the end of the recommeded wash time. Note that the overall time will be about the same for the two variations but the Ilford method will use less water. So, the Ilford method is superior where water conservation is the objective, the Kodak method is more convenient because only a single time interval must be remembered. As far as washing efficiency both methods provide for a decreasing concentration of hypo in the wash water as washing progresses.
   Both methods will wash hypo down to any required level.
Because a sulfite wash aid greatly increases the wash rate it is strongly recommended where conservation of water is necessary. For film the ratio of wash time is about 6 times where a normal acid hardening fixer is used. The ususal wash time recommended for film is about 30 minutes in water no colder than 68F (52C), when a sulfite wash aid is used this is reduced ato about 5 minutes. The times are applicable to both running water and progressive bath methods.

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


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