Archived posting to the Leica Users Group, 2005/11/23

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Subject: [Leica] Ups and downs of stop baths?
From: keirst at fas.harvard.edu (Steven Keirstead)
Date: Wed Nov 23 08:50:00 2005
References: <4cfa589b0511221455w1de5d0d0p160703dbc594a087@mail.gmail.com> <p06230901bfa95e7366e0@[10.4.1.128]> <6.1.0.6.2.20051122163219.05de5b70@192.168.100.42>

>From what I have read, a long time ago Kodak and 
other manufacturers had different gelatin and 
film bases that were not as cohesive as modern 
films and emulsions. The gelatin was softer, 
weaker and could tear more easily. Sometimes when 
the developing film went from a carbonate 
buffered developer into an acid stop bath, CO2 
was formed by acid-base reaction from carbonate 
and the effervescence in the would tear gelatin 
specs off the film base, leaving a clear spot in 
the negative. This would be more likely to happen 
if the temperature was above 68?F (20?C) for the 
process solutions. Modern films have pre-hardened 
gelatin, so this is less likely to happen now, 
unless you are working in tropical temperature 
conditions.

If you are making your own developer solutions, 
you can switch to a Borax or Borate buffering 
system, which will not effervesce. There may be 
commercial developers with Borax buffer, but I 
don't know of them.

While there may be some developers that are 
acidic or continue to have some activity in acid, 
most are still carbonate buffered, and the pH 
change and developer dilution of putting film 
into a stop bath ensure a precise end to 
development, while water alone may allow more 
continued development. I usually use a 1.5% 
Citric acid stop bath. A 15% (or 30%) Citric acid 
stock solution seems to be quite stable, does 
appear to grow microbes, does not smell like 
acetic acid and is quickly diluted 1:9 from 15% 
(or 1:20 from 30%) for working stop bath.


>At 04:05 PM 11/22/2005, Henning Wulff wrote:
>
>>The main problem is that pinholes can develop. 
>>If you do use any 'stop bath', dilute it a lot.
>>...

Richard <richard-lists@imagecraft.com> wrote

>What exactly are pinholes? Actually holes in the negatives or the emulsion?
>

-- 
______________________________________________________________________________
Steve Keirstead
Research Assistant II, Biology Teaching Labs,
Harvard Science Center, Room 409, 1 Oxford Street, Cambridge, Ma 02138.
Work Phone: (617) 495-2683 , FAX: (617) 496-9105


Replies: Reply from rhaightjr at yahoo.com (Bob Haight) ([Leica] Ups and downs of stop baths?)
In reply to: Message from abridge at gmail.com (Adam Bridge) ([Leica] Ups and downs of stop baths?)
Message from henningw at archiphoto.com (Henning Wulff) ([Leica] Ups and downs of stop baths?)
Message from richard-lists at imagecraft.com (Richard) ([Leica] Ups and downs of stop baths?)