[Alt-photo] Sodium Thiocyanate For Fixing Out Lumens

Ryuji Suzuki rs at silvergrain.org
Tue Aug 15 17:51:11 UTC 2017


You might want to get a copy of this paper if you like to see what's 
known in situations that are somewhat close to what you are doing. 
Without chemical development process you don't have filaments but you 
can probably learn from what happens to the smallest grain, thinnest 
filament condition among what he studied. Abstract is from uncorrected 
OCR, sorry about some errors.

The Stability of Silver Filaments
T. H. JAMES, Research Laboratories, Eastman Kodak Company, Roch:ester, 
N. Y. 14650

PHOTOGRAPHIC SCIENCE AND ENGINEERING Volume 9, Number 2, March-April 
1965

The effeds on the strudure of the developed silver of storage at high' 
humidity and of treatment with various salt solutions were studied on 
several bromide emulsions. An over-all increase iii transmission 
density, with some decrease in refledion density, occurred with 
fine-grain emulsions within a few hours upon storage at approximately 
100% relative humidity at 21°C. Similar changes occurred more rapidly 
at higher temperatures. 'The changes were more pronounced with unfixed, 
fully developed film than with fixed film, and the changes in density 
wete accom- panied by a thickening and breaking up of the filamentary 
strudure and an increase in crystal- lite size. Similar changes in 
filament strudure, and a decrease in refledion density, occurred for all 
chloride, chlorobromide, arid bromide emulsions tested, but IiHle or no 
change in trans- mission density was observed when the original silver 
halide grain size exceeded about 0.4 ",. Iodide, whether derived from 
the processing solutions or from the development or fixation of the 
silver halide grains, retarded the changes. A rapid conversion of 
filaments into nonfilamentary, rounded particles occurred in the 
chloride, chlorobr9mide, and bromide emulsions when the unflxed, 
developed film was immersed in a 1%or stronger.solution of a thiocyanate 
or chloride. The degradation of the fllaments was retarded by iodide and 
thiosulfate, by the presence of strong reducing agents, or by stringent 
exclusion of oxygen, but it did occur readily under the
laHer condition when silver ions were added to the solution. The 
degradation of the fllaments appeared to be a recrystallization 
phenomenon, and a mechanism based on local cell action was suggested.


Regarding the fixing mechanism of sodium v ammonium thiosulfate, and 
thiocyanate, see

The chemistry of fixing I. Silver complexation by thiosulfate anion
M.R.V. Sahyun, Imaging Research Laboratory, 3M Company, St. Paul, 
Minnesota 55101
PHOTOGRAPHIC SCIENCE AND ENGINEERING· Volume 17. Number 2. March/April 
1973 Reprint Number 7326

The chemistry of fixing II. Silver complexation by thiocyanate anion
M.R.V. Sahyun, Imaging Research Laboratory, 3M Company, St. Paul, 
Minnesota 55101
PHOTOGRAPHIC SCIENCE AND ENGINEERING. Volume 17. Number 2. March/April 
1973 Reprint Number 7327

Chapter 5 of James's 1977 book is also an excellent reference. (The 
chapter written by R. W. Henn)

Finally, be careful about thiocyanate as a fixing agent. As James's 
paper shows, it can change the morphology of the silver image, and you 
want to control the residue very carefully. Also, strong thiocyanate 
solution damages gelatin and weakens the mechanical properties and 
perhaps long term durability. I think it is probably wise to formulate a 
fixing solution that is primarily based on thiosulfate but uses a 
pre-bath or an additive to alter the image tone as desired. The topic of 
image tone was a very common one for the radiographic film emulsions and 
their developer formulation. Very numerous patents issued, with very 
many compounds named (but in reality, I bet only a few used in 
practice).

Ryuji Suzuki
"Don't play what's there, play what's not there" (Miles Davis)

On 14 Aug 2017, at 14:00, Andy Duncan via Alt-photo-process-list wrote:

> Hi all,
>
> I’m experimenting with different ways of fixing lumen prints, and 
> read
> somewhere (I think in a thread on apug.org) that sodium thiocyanate 
> can be
> used to fix out prints. I've used Ilford Rapid Fix in the past, but my 
> main
> fixer in recent years has been TF-4 from Photo Formulary, which is 
> what I
> use for my film. The color shifts from both were pretty similar, both 
> being
> ammonium thiosulfate. I began using the sodium thiocyanate recently, 
> and
> after my last batch of prints, I noticed that after processing, some 
> of the
> prints continued to darken. I processed in a 5% dilution for 1-2 
> minutes (I
> don't get real scientifically accurate with my times when processing
> lumens...maybe that's part of my problem); the source I first read 
> that
> mentioned using sodium thiocyanate gave a 10% dilution. So my question 
> is
> this: is sodium thiocyanate as permanent of a fixer as the other 
> fixing
> agents in TF-4 and Ilford Rapid Fix?
>
> I was also wondering if any of the chemists out there could explain in
> layman's terms the difference between sodium thiocyanate and ammonium
> thiosulfate? What is the effect each has on image permanence and
> stabilization?
>
> I suppose I should add that I'm not afraid of the color shifts that 
> occur
> after fixing a lumen print, nor are they unwanted. On the contrary, I 
> tend
> to welcome them. I just want the lumen to be as permanent as I can 
> make it.
> I'm starting to prefer the shifts that occur with the sodium 
> thiocyanate
> over those that occur with TF-4, so I'd like to make sure they'll be 
> as
> stable when processed in TF-4. I have prints that are 10+ years old 
> that
> have had no further shift in color/intensity/brightness after being 
> hung on
> my walls. These recent ones shifted only hours after being taken off 
> my
> drying racks.
>
> Thanks in advance!
> Andy
> _______________________________________________
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