[pure-silver] Re: re-using DDX


----- Original Message ----- From: "Shannon Stoney" <sstoney@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, March 31, 2006 10:28 AM
Subject: [pure-silver] re-using DDX


I was reading the DDX bottle today and noticed the following:

"For economy, DDX can be reused to process either a number of films individually or multiple films in batches. If a series of films is being developed in a spiral tank, compensate for the loss of development activity after developing the first film (or batch of films) by increasing development time 10% for each successive batch. This relies on the used developer...being poured back into the working strength solution's storage bottle and mixed with the fresh, unused part of the developer before processing the next film/batch."


??? I don't get it. Pour the used developer back into some fresh working solution and then add 10% to your times? But, how much fresh developer? And how does that save any money if you need fresh developer to do it?

--shannon

It is a bit indefinite.
Most developers can be used for more than one roll or batch of film by extending time. Usually, there will be a loss of shadow detail because of the accumulation of reaction products. To a large degree this can be compensated for by replenishment. Older developers use a separate replenisher solution, some later developers are replenished by adding more developer. T-Max RS is an example of this type. I beleive Xtol can be replenished the same way.
For simple replenishment the replenisher is added according to the area of film developed, the amount of developer being carried off by the film assumed to be enough so that the volume of the developer remains constant. This method works better than simply re-using developer, however, for consistency sensitometric tests must be made periodically. This last is how photofinishing machines and motion picture developing machines are operated. There is still a difference between fresh developer and replenished developer. In automatic machines a "developer starter" is used to condition fresh developer to minize the difference when new developer is being used. The starter adds what amounts to reaction products to the fresh developer. This method is simply too bothersome for low volume home darkrooms.
You are right to be confused by Ilford's instructions since the effect on development time on re-use depends on the volume of used developer to the volume of fresh developer. For instance, a single 8 oz tankfull of used developer when added to 5 liters is likely to have insignificant effect.
Ilford used to be pretty good at answering e-mail, it would be worth a few minutes writing to them for clarification.

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

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