A lot has been written about the staining qualities of cafenol. Like much of what has been written some of it is true, some is exaggerated and some is plain BS.
A while back a gentleman asked if Cafenol would stain his developing tanks. This was kind of a surprise, and the answers he got was more of a surprise. I have watched out for stains from Cafenol since day one, and this is my take on the situation.
- Cafenol contains massive amounts of washing soda. In itself this is a very strong cleaning agent, back in the day this was what my grandmother used to get rid of nasty stuff from cleaning out fish - she came from a fishing village on a small island. Only stronger stuff she ever used was lye - but then only in emergencies!
Since we have concentrated soda in the mix, borth organic and inorganict matter will be dissolved and lifted into solution, given time and repeated exposure.
The relative small amount of coffe, containing caffeine and caffeic acid, among a mix off other stuff is said to have staining abilities. So will the coffe stain the plastics in developing tanks, or will the soda negate this?
The coffee component will stain photograpic film - to some degree. I have noticed this effect stronger in color films than in B&W films (which is what can be expected), Cafenol will develop most C41 color films jkust like most B&W films.
Recent experiments with Fomapan and Lucky 100 B&W films in Cafenol C-H did not show staining to any degree, straight scans came out nearli pitch dark in the shadows and clear in the hight-lights, the same for TriX, even if my TriX was more than 35 years old and did show considerable chemical fog, it scanned perfectly, however.
And older test with coffe & soda alone, sans vitamine C did show markedly higher stain levels - this probably was connected with the fact that development times had to be increased (doubled) and concentration of the coffe doubled or tripled, because coffe is such a weak developing agent on its own...
Staining in the film works differently from staining of plastics: coffe gets sucked up into the gelatine layer and stains whats inside THERE, personally I think this has to do whith gelatine, more than anything else.
When it comes to developing tanks, few pause and think through what is at hand here.
Developing tanks are made from what is to be stain-free plastics. However we all know and have seen old spirals blackened from developer.... So what exactly causes that?
There are very few modern-day staining developers, in earlier days, and among a few enthisiasts, amidol-based developers are noted for staining qualities. Cafenol is nothing like that.
Besides more than 90% of the stains seen on developing tanks stems from quite another mechanism than the developer :
The stains comes from the fixer. To the casual observer the fixer does one thing: dissolves unexposed, undeveloped silver-halides. Few knows that the exact mechanism that this takes plave varies wildly with both concentration and the dissolved silver in the fixer solution.
Again I have to direct interested partied to my german-language tome :
"Wissenshaftliche und Agewante photographie" von Edwin Mutter, Springer Verlag 1955, page 181.
Fixation takes place in four discrete steps, the first two leaves insolulble silver-sulphur complexes in solution, but as long as the silver concentration is low, and the fresh hypo-concentration is high, the fixing process runs to completion for two more steps and leaves soluble silver salts in solution. This is what normally takes place as long as the fixer is not exhausted.
If we work with exhasuted fixer, this process doesn not run completely or very slowly, leaving us with fixer stains.
This is what we find in developing tanks, its got nothing to do with the developer.
Alswo sloppy procedures, to little washing and not properly cleaning the tanks will give rise to such stains, with a little bit different mechanism : if we leave fixer on tank parts, they will of course dry out. As the fix droplets dries, concentration changes in them, if there's enough silver in there, the silver concentration will outrun the hypo concentration, and silver-sulphur complexes will fall out and stain the surface.
This can be seen as brown fingerprints, where spirals, lids etc have been handled with fixer-stained fingers.
IF WE START USING CAFENOL IN STAINED TANKS LIKE THIS, CAFENOL WILL DISSOLVE THE SILVER-SULPHUR HALIDES, SLOWLY WITH TIME AND REMOVE THEM!
THis was brought home to me by 3 Jobo 1000 tanks I got used on €-bight. Theu all came well used, with one or two stained spirals and 3 stained lids. The word JOBO was written in black, from silver fixer stains.
Now after continued use as cafenol-tanks for more than a year, and well used as that might I add, all of the brown-black stains on the lidsa have disappeared, caffenol has cleaned them, I never tried to do anything special, just used them as normal and washed meticously as I always do with films.
The spirals are much cleared too, but difference in the plastic used (more transparent and brittle than the flexible lids) probably makes for this to take a considerable time to clear.
Finishing off : You can safely develop all kind of films in Cafenol, the tanks are designed for it, and high concentration of a strong detergent in the deeveloper, washing soda will clear smudges and stains from previous use.