[pure-silver] Re: re-using DDX

From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: re-using DDX
Date: Fri, 31 Mar 2006 11:19:55 -0800

>    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.

Firstly, Shannon's post was concerning about reusing the
developer, not replenishing. it. Replenishing is irrelevant here.

Secondly, it has nothing to do with old or modern formula whether the
a developer is used with a matching replenisher (or the developer is
made from the replenisher with a starter seasoning).

>    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.

Top-up method described here is not as consistent as bleeding system.

Bleeding system is not maximally economical, as in the case of top-up
method, but high quality image can be obtained with much less chemical
waste than one-shot use.

> This last is how photofinishing machines and motion picture
> developing machines are operated.

This is not necessarily true in past few decades. Since London dumping
convention (1990s), photographic industry can no longer dump its
waste solution to ocean, and therefore all waste solution must be
collected and burned. This increased the cost of chemical waste
disposal, and companies like Konica and Noritu worked hard to minimize
the volume of the waste solution from minilab machines.

Most processing machines and volume processing establishments use a
device equipped with an rejuvenator. This takes a fixed portion of the
developer each time so many rolls are processed, and feed it through
an ion exchange resin, which removes bromide ion from used developer,
which is fed back to the developer tank.

> 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.

It is not too bothersome. It can simply done in a small tank.

The problem is lack of correct knowledge of how replenishing system
works.
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