[pure-silver] Re: PMK

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Fri, 28 Apr 2006 03:05:35 -0700


----- Original Message ----- From: "Georges Giralt" <georges.giralt@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, April 28, 2006 2:24 AM
Subject: [pure-silver] Re: PMK


Jim MacKenzie a icrit :

----- Original Message ----- From: "Hagner, Andrew" <Andrew_Hagner@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, April 27, 2006 4:39 PM
Subject: [pure-silver] Re: PMK


Other than for use with PMK, what are the advantages (if any) of an all
alkaline process for film development.
===
You need a much shorter wash and can forego a hypo-clearing agent step.

Alkaline-fixed film needs about five minutes of wash to be archivally processed, without any washing aid needed.

Jim
Hi !
If you follow the Ilford washing sequence, you only need 5 minutes to was your film, without was iad, and whatever fixer you use.
Test had been done which show that washing for film is best done by frequent change of water with agitation than letting the film soak in a more or less stagnant water.
Jobo advice the same when they state that you've to wash using 30 sec. cycles in their CP processors.
And, last but not least, you SAVE water which is becoming scarse.
Enjoy
--
I think think there is some misinterpretation here. Ilford does suggest a method of washing using sequential changes of water but the total time is the same as for a running water wash. Kodak has a similar method but it differs from the Ilford method in that the time for each change is the same while Ilford uses short periods at the beginning, when the hypo is leaving the film rapidly, and progressively longer washes as the washing continues. Both are effective but the Ilford sequence probably uses less water.
Washing is fastes when there is a continuous, rapid change of water at the surface of the film. The emulsion washes out by a diffusion process, the rate of diffusion depends on the concentration of hypo in the emulsion vs: the concentration in the wash water. Washing is very rapid at first and slows exponentially. Thats why its important to use fresh water toward the end of the wash.
Sequential changes of water are no more effective than running water but are economical of water and useful where there is no running water.
The use of a sulfite wash aid substantially increases wash rate regardless of fixer type and is important where economy of water use is important.
When a hardening fixing bath is used a running water wash takes about half an hour. Sequential changes of water should take about the same time. When a non hardening, neutral pH fixer is use wash time is about 10 minutes. When a 2% sulfite bath is used wash time is about 5 minutes regardless of the fixer type.

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

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