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Friday, August 7, 2015

Still about using salt as fixer for films

Although salt has been used in the past to fix daguerreotypes, it became then a myth among photography hobbyists. People who tried it, didn't know were to start when preparing a salt bath that possibly could fix the films used today.

I like testing if myths are true or false. So, and because at the time I was experimenting with daguerreotypes too and reading how it worked, I decided to try whether salt was able to fix modern films.

I was using at the time Fomapan and Shangai GP3, the cheapest on the markt.

Intuitively, and after I tried a randomly dissolved salt solution, some grams per liter (don't know anymore), and this didn't work in a reasonable time span, I decided to make the more concentrated solution I could and wait the longest time I could consider reasonable, the whole night. If we develop films at night, this is a time that will not affect our patience because we are sleeping.

So, after some time shaking a PET bottle full with salt and water, I putted a stripe of virgin film in a bowl and poured the salt water on it and went to sleep.

Next day, the stripe of film was completely transparent, what showed me that salt as fixer is not a myth, but it does make the job.

Further investigation showed me that if the salt solution is enough concentrated and warm it will take less time to work. For films like Fomapan, Shangai GP3, Ilford FP4 or HP5, it is possible to completely fix with salt in 3 hours, using 300 g/l of salt and temperature above 30ºC.

All my tests and results were made publicly, at Flickr. This all happened 3 years ago, in 2012. Since then, nobody spoke about, as far as I know. Recently, at the forum of Filmasters.com there was a discussion about it were salt as fixer was not a myth anymore, meanwhile my results were spread, thanks to Reinhold and trough his fine blog Caffenol

Some days ago, someone wanted to see pictures I made and fixed with salt. But because these pictures were at Flickr, where I closed my account, but I found this information at ipernity were I have an account now: http://www.ipernity.com/search/photo?w=303455&q=salt&view=2

Cloud festival
Fixed with salt
Well, but the introduction took too long and what I wanted to bring you today are some more information on how to better use salt as fixer and this is particularly interesting for countries were travelling with chemical stuff is very illegal and old fashion photographers will have troubles with the law.

When preparing salt fixer, be aware to dissolve as much salt you can. 300 g/l, if you succeed, will do the job. Use warm water and try to get it all dissolved.

The next, pass the solution through a coffee filter. This step is important, as I found recently. Not only to retain some impurities of the salt but to prevent that small and invisible undissolved salt stay in the solution. These salt particles are, I think, responsible for the rapid formation of salt crystals that may affect your emulsion during fixing. They may produce holes in the emulsion. A filtered solution will not produce crystals for more than 24 hours, the time you may need to fix the film.

Another improvement is adding to the salt fixer some grams of Potassium Bromide which is a veterinary medicine easy to get. 5g/liter are enough. Potassium Bromide will speed up the fixer and it will also delay the crystallization of the salt as I observed now.

24 hours fixing

48 hours fixing

Testing with drops of pure Rodinal 
Legend:

Kodak TMax-400 stripes «fixed» with salt.

On the left side I used only salt, in the middle salt+potassium bromide and on the right salt+potassium metabisulfite.

I didn't use temperature in this experiment.

Results:

The bowl with just salt already started crystallizing. The others not. The stripe on right acquired a brownish stain and is not better fixed than with just salt, but metabisulfite also prevented crystallization. Maybe other salts will also do it.
It is clear that the stripe in the middle, with Potassium Bromide, is better fixed than the others, after 48 hours. But not completely fixed yet!!! If so, no stain would appear after droping Rodinal pure on it.

Note:

Kodak TMax and similar films (T grain), multicoated films, are more difficult to fix. Even using regular Rapid Fixer, you would better let it for 30 minutes instead of just 2 minutes. Once I had some drag marks with Rapid Fixer and refixing for 30 minutes solved the problem. The fixer was not that new.

I might try to improve the results. making it possible to fix completely TMax films with salt.

2 comments:

IH said...

@Chronocrator,
I believe the fixing comes from the minute solubility of silver halides, and the salt ions cl- and br- might facilitate this by attacking the Ag atom in the AgHL and swap with the halide atom, so a saturated NaCl and KBr solution might have the best effect. Also if this hypothesis is true, this solution will never exhaust its fixing power, but you'll have to filter the AgHL off from time to time. but hey I'm a biochem major so not really sure about this :p
Cheers,
Ian

Henrique Sousa said...

Thanks for commenting and for your interpretation. Very interesting the non-exhaustion that need still to be tested.
Salt is very cheap and available everywhere. It does the job for the most films and does half the job with more resilient films. It is an alternative in certain difficult situations like beeing in places where you can't buy chemicals and you are not allowed to bring them. But even beeing a bad fix it is a fix and once at home films may be refixed in regular fixer.
If it could be improved with common available stuff that would be great.