[pure-silver] Re: Yellow edges
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 24 May 2005 07:09:56 -0700
----- Original Message -----
From: "Justin F. Knotzke" <jknotzke@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, May 24, 2005 6:29 AM
Subject: [pure-silver] Re: Yellow edges
> On 5/24/05, DarkroomMagic <info@xxxxxxxxxxxxxxxx> wrote:
>
>> 2. Exposure to white light before fixing was complete.
>
> Ooh. I do that. All the time. I often flick the lights
> on as soon
> as the paper hits the fixer. I've been doing that for a
> year or so
> with no real problems. But yesterday, as I stated, I
> forgot the stop..
>
> Ok, next batch, I will do Richard's test and I will make
> sure to
> not flick the lights on before the fixing is finished..
>
> Thanks for the reply.. I think that might be it.
>
> J
>
>
> --=20
> Justin F. Knotzke
> jknotzke@xxxxxxxxx
> http://www.shampoo.ca
Turning on the lights too soon in threory can cause some
photolytic silver to be produced. I think in practice, with
normal room light, this would be insignificant. Acid fixer
inactivates the developer nearly instantly and also
desensitizes the remaining emulsion. Its probably safe from
a fogging standpoint to turn the lights on a few seconds
after putting the print into the fixing bath although the
rule of good practice is not to turn them on until fixing is
halfway complete.
Without some testing its impossible to say what exactly
went wrong but my best guess is a combination of the lack of
an acid stop bath and exhausted fixing bath.
Most B&W fixing baths are acid even if they do not contain
a hardener. The usual acid fixing bath has a very good
buffer system to maintain the pH even with the carryover of
substantial developer. Also, acid fixing baths _must_ have
an excess of sulfite to prevent decomposition of the
thiosulfate by the acid. The sulfite also serves to prevent
staining from developer reaction products from carried over
developer. Most of the standard fixing baths derive from
formulas dating from the mid 1930's, a time when it was
common practice to use water rinses or no bath at all
between developer and fixer. The baths were designed to
withstand substantial carryover of active developer without
the pH window moving out of the range where the hardener was
effective or the production of staining. It is still bad
practice not to use a stop bath but the fixing baths
generally will withtand it.
Capacity of single fixing baths to produce archival
fixing is very limited. Fixing of the undeveloped silver
halide is a process that makes it water soluble. Much of it
comes out in the fixing bath, some in subsequent washing.
The fixing process actually goes through several steps, each
producing a more soluble complex than the last. It takes a
substantial amount of free thiosulfate ions to completely
complex a silver halide ion so that it will wash out. In
incompletely fixed emulsion some of the silver-thiosulfate
complex is such that it is still insoluble or else so
tightly bound to the emulsion or image silver than it won't
come out in washing. The residual complexes will eventually
decompose causing staining and may attack the image silver.
This sometimes takes years. Fixing baths can fix enough to
make prints or film stable for many years but not for
archival standards. A two bath fixing system insures that
the second bath will have enough free thiosulfate in it to
complete the fixing process. The capacity of a two bath
system to fix archivally is from four to ten times that of a
single bath.
The only real test of fixing is to test a film or print
using a Sodium Sulfide test solution, or, with some
limitations, the Selenium toner test solution.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
