[pure-silver] Re: re-using DDX


----- Original Message ----- From: "Ryuji Suzuki" <rs@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, March 31, 2006 2:09 PM
Subject: [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.


A couple of things.
I understand what Shannon was asking about and described
replenishment to distinguish it from simply reusing it. It
is relevant to the thread.
I stated that two kinds of solutions were used for
replenishment: 1, a special replenisher formula; 2, the
developer itself. The process or replenishment is the same
for both.
Ideally, the method of replenishment should maintain
developer properties constant. This is determined for large
scale machine processing by frequent sensitometric testing
and by chemical analysis. It is this kind of control I meant by being too bothersom for small volume home darkrooms. Now, some people do a lot of color work in semi-automatic machines, like the Jobo, probaby testing like this becomes reasonable and desirable at that point.
Motion picture machines, which are very large scale, use
both replenishment and chemical regeneration of the
solutions as you point out. This includes both filtering and
the use of silver recovery. In color processing virtually
all the silver used in the film can be recovered. In a large
scale motion picture plant this is very considerable.
I talked briefly to someone at Deluxe Labs a while back.
They work under very stringent environmental protection
conditions, especially about waste water. Almost everything
is recycled.
Release prints for major motion pictures run to over a
million feet of film which will give you a hint at the
yearly volume of labs like Deluxe, Technicolor,
Consolidated, etc.

Since others may have misinterpreted my post your comments are a welcome chance to make things clearer.

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

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