[pure-silver] Re: washing film with deminarilised water
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 1 Mar 2005 16:28:21 -0800
----- Original Message -----
From: "john stockdale" <j.sto@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, March 01, 2005 5:02 PM
Subject: [pure-silver] Re: washing film with deminarilised
water
> Thanks, Jerry.
>
> Unfortunately here at the end of the Earth (Australia)
> chemicals tend to be
> more expensive than in the USA. Here sodium sulphite is
> 2.5 times the
> price of sodium bicarbonate in 25kg bags.
>
> (The sodium bicarbonate offered is more pure (food grade)
> than the sodium
> sulphite which is "photo grade= 98.5%", but that's what is
> locally available)
>
> On a happier note, Dimezone-S is much cheaper than in the
> USA, but maybe I
> was lucky.
>
> I always use sulphite washing aid. My question was about
> the efficiency of
> washing in subsequent baths, which are usually plain
> water. It has been
> noted that some bicarbonate facilitates washing in those
> subsequent
> baths. I was wondering what the optimum use of the two
> chemicals is. It
> is relevant here since I'm building a darkroom in rural
> Australia where
> water use must be minimal.
>
> John Stockdale
As far as I can tell from the paper published by Kodak on
sulfite wash aid (I'll find the citation) the nature of the
water used after treatment is of little importance. The
sulfite aid also allows the use of colder water for washing.
The researchers tested a number of salts. While several
accelerated washing none was as effective as sulfite.
Kodak's commercial product is buffered to neutral pH in
order to minimise swelling and to preserve hardening from
alum hardener. The buffer is sodium bisulfite. It also
contains some EDTA tetra sodium salt and some sodium citrate
probably to prevent deposits of minerals from the water or
to prevent a sludge from forming where the wash aid is
reused.
Sulfite has a specific effect as an ion exchange agent in
addition to its alkaline pH. It is this ion exchange
property which makes it far more effective than treatments
in alkaline salts like carbonates.
A formula which I believe to be the actual formula for
KHCA is:
Sodium Sulfite 100.0 grams
Sodium bisulfite 15.0 grams
Sodium Citrate 5.0 grams
EDTA tetrasodium salt 5.0 grams
Water to make 1.0 liter
It is possible the EDTA and citrate should be 1.0 gram.
Dilute the above 1 part stock to 4 parts water for use.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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