[rollei_list] Re: OT: development
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 21 May 2005 18:57:00 -0700
>> ---
>> Rollei List
>>
> You're right Richard, half the elegance of the two bath
> system is how the
> second bath after doing a full cycle becomes the first
> bath and is good for
> another full go all over again! How often does a thing
> like that ever happen
> in my life? Never!
>
> That would not be logically possible if your second bath
> and first bath were
> not the same stuff.
>
> Also there's that interesting aspect as to a process that
> get started in
> Ammonium Thiosulfite but then taken over by Sodium
> Thiosulfite might have
> some strange effect. Like Lily Tomlin in "The Incredible
> Shrinking Woman"
> being exposed to conflicting household products while
> washing her kitchen.
>
> I use Sulfite instead of hypo clear.
> According to Dignam it's the main active component in the
> stuff anyway.
> Other than I think some Sodium Bisulfate which acts like a
> hardener.
>
> Do I want hardener in my softener?
> And pay though the nose for it and have to stock it?
> So I just use a coffee measure of sulfite in a tray. For
> over 20 years.
>
> I better go check my prints! :)
>
>
>
> Mark Rabiner
> Photography
> Portland Oregon
> http://rabinergroup.com/
>
I truely do not trust Dignan's stuff.
Kodak Hypo Clearing Agent working solution is about 2%
Sodium sulfite. The sulfite acts as both an alkali and as an
ion exchange agent. It is its efficiency as the latter that
makes it desirable as a wash aid. The bisulfite (probably
actually metabilulfite) acts as a buffer. In addition there
are two sequestering agents to prevent sludging: Sodium
citrate and EDTA tetra sodium salt.
The purpose of the bilsufite is to buffer the mixture to
neutral pH. Kodak does this so that hardening from white
alum is preserved and emulsion swelling is minimised. At
neutral pH the binding effects of alum and the binding
effects of the electric charges in the emulsion on
thiosufate and fixer reaction products, is eliminated. The
minimum swelling makes the diffusion path minimum and
probably makes the emulsion less vulnerable to damage during
washing.
A plain sulfite bath is about as effective but will
destroy the hardening from white alum. This is of no
consequence when a non-hardening fixing bath is used. The
sequestering agents seem to be necessary only if the working
solution is to be reused.
There is no published formula for KHCA but the following
is close:
Wash Aid Stock
Water, 750.0 ml
Sodium Sulfite, dessicated 100.0 grams
Sodium bisulfite 20.0 grams
EDTA Tetra sodium salt 5.0 grams
Sodium Citrate 5.0 grams
Water to make 1.0 liter
For use dilute 1 part stock with 4 parts water and treat for
from 1 to 3 minutes with agitation. then wash as after KHCA.
Film 5.0 minutes
Single weight paper 10.0 minutes
Double weight paper 20.0 minutes.
If the solution is to be reused the capacity will be
extended by rinsing film or paper for 30 seconds between
fixer and wash aid bath.
Since Kodak practice is to specify Sodium bisulfite where
sodium metabisulfite is meant the metabisulfite will
probably work as well and is much cheaper and easier to
obtain.
The sequestering agents may not be necessary to the wash
aid function but are included by Kodak to prevent sludging
when the working solution is re-used. If it is to be used
one-shot they are probably not necessary.
I suspect there is a patent covering this, I would love
to find it.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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