Stop and fix time

[kkcsm]

Advertisement (gone after registration)

I’m pretty new to home developing.  I’ve been sticking to massive dev chart times.  My question for you experts:

Is the time for stop bath and fixing critical?

Developing time and temp is critical as there is a chemical reaction that can go too far or not far enough.  However, once something is stopped or fixed, it cannot be more stopped or more fixed. Can I be a bit sloppy with those steps wrt increasing time?  Or can film be over stopped or over fixed?

-K

[adan]

No, stop and fix time are not as critical as development.

It is technically possible to "overfix" film - the fixer chemicals, which are slightly acidic (acetic acid = purified vinegar), can start to dissolve the developed silver image as well as the unexposed, undeveloped silver.

But that takes an extremely extended time - 30 minutes or more (maybe much more) to see much effect, compared to the 4-10 minutes for normal fixing.

However, fixer is temperature-sensitive - its effectiveness drops off dramatically below 65°F/18°C. Which is why 68/20 is the normal "base" processing temperature for B&W films.

Stop bath is also acidic (again, acetic acid), and has two jobs to do. The "stopping" function - wherein the acid neutralizes the pH of the alkali in the developer left on the film - is done in a matter of seconds (or else why bother - the idea is to stop the developer activity right now, to the second). The second function - to completely neutralize any remaining developer so that it doesn't de-acidify the fixer and make it less functional - takes not much longer. 30 seconds is easily enough, but 1 minute won't hurt anything. But there's not a lot of point in going any longer - it just means more time before you get to play with the dry negatives.

[kkcsm]

Thank you Adan, exactly what I was looking for.  With developer I can get the temperature just right.  But stop/fix are pre-mixed and consequently are the temperature of wherever they're stored.  Nice to know I can kind of ballpark things to take that into account rather than trying to be perfect.

-K

[Richardgb]

On 7/2/2019 at 5:34 AM, adan said:

No, stop and fix time are not as critical as development.

It is technically possible to "overfix" film - the fixer chemicals, which are slightly acidic (acetic acid = purified vinegar), can start to dissolve the developed silver image as well as the unexposed, undeveloped silver.

But that takes an extremely extended time - 30 minutes or more (maybe much more) to see much effect, compared to the 4-10 minutes for normal fixing.

However, fixer is temperature-sensitive - its effectiveness drops off dramatically below 65°F/18°C. Which is why 68/20 is the normal "base" processing temperature for B&W films.

Stop bath is also acidic (again, acetic acid), and has two jobs to do. The "stopping" function - wherein the acid neutralizes the pH of the alkali in the developer left on the film - is done in a matter of seconds (or else why bother - the idea is to stop the developer activity right now, to the second). The second function - to completely neutralize any remaining developer so that it doesn't de-acidify the fixer and make it less functional - takes not much longer. 30 seconds is easily enough, but 1 minute won't hurt anything. But there's not a lot of point in going any longer - it just means more time before you get to play with the dry negatives.

Just to add to Adan's post, the usual recommended fixing time is 2x the time it takes for the film to 'clear', i.e. the cloudiness of the undeveloped emulsion has disappeared. As the fixer is used (both it an stop bath are re-usable and easily stored), the time to clear gets longer. Once the clearing time is taking twice as long as when fresh, discard the fixer and use fresh.

For more critical work where longevity is critical, 2-step fixation is recommended: The first bath is used until the film clears, then a second bath used for the same length of time. One the first bath takes twice as long as it did to clear the film, discard it and use the second bath in its place. Mix new fixer for the second bath.

For typical home use, it's usually OK to dispose of used fixer (which contains dissolved silver) into the domestic sewage system. If you have the space to store used fixer until you have enough of it, you might be able to interest a metals-processing company to recover the silver which they sell on the market. It's highly unlikely you'd make any money doing so, though! A 'party trick' you might find amusing is to drop a 'copper' coin into used fixer and see it get covered in silver, but don't use the fixer afterwards for processing!

[pico]

Consider the significant differences between common fixer and ammonium thiosulfate, or so-called Rapid Fix.

[otto.f]

On 7/2/2019 at 5:35 AM, kkcsm said:

Or can film be over stopped or over fixed?

A film can be underfixed though, so I’d follow Richardgb’s advice on two-step fixing. I use two bottles, I refresh bottle1 after a few films and then use bottle2 for the first bath and bottle1 for the second, etc. 

[M.Hilo]

Advertisement (gone after registration)

On 7/2/2019 at 4:37 PM, kkcsm said:

Thank you Adan, exactly what I was looking for.  With developer I can get the temperature just right.  But stop/fix are pre-mixed and consequently are the temperature of wherever they're stored.  Nice to know I can kind of ballpark things to take that into account rather than trying to be perfect.

-K

If you're talking about film developing, all three chemicals and the first water washing should be the same temperature. With washing you can then slowly let the temperature drop . . .

[kkcsm]

I just took the temperature of some distilled water stored next to my chemicals, 20c. So, fine if I’m developing there.  But if I’m developing at 24c, what is the effect of stopping and fixing at 20c?  Or increasing the stop and fix time a few percent to compensate?  Or increasing stop and fix time because I’ve used those chemicals 6 or 8 times previously?

[adan]

In theory, going from warm (24C) developer to colder (20C) stop-bath can cause reticulation, and/or an increase in grain.

The deal is that the gelatin coating that contains the silver swells when wet, and swells even more when warm and wet, and swells even more if warm and wet for a long time (extended development) - and plunging it into cooler liquid can cause it to contract, and shrivel, and that can cause a craquelure pattern to be permanently formed in the gelatin.

And/or allow the silver grains to migrate around a bit in the warm soft gelatin.

If you're from KS, you've probably seen some clay-bottomed streams that dry out in the summer, and the clay cracks into little polygons as it dries and shrivels - kinda like that.

https://www.alamy.com/stock-photo-baked-clay-drought-dried-river-bed-cracked-mud-37417932.html

https://www.ilfordphoto.com/unleash-that-reticulated-film-python/

Now to some extent that is an old theory from films prior to 1970 or so (and before central heating and cooling - where a darkroom might be excessively cold in winter or hot in summer - or if trying to process out in the wild with stream water or some such (it has been done!)). These days it usually takes far more temp. change that 4°C to create reticulation. The manufacturers have toughened the gelatin used, to minimize the possibility. That Ilford link mentions two extreme temperature changes of 100°F/38°C to get it to happen intentionally. And the thinner Delta/Tmax films are even less susceptible.

If you stay within the temperatures normally listed for developing (20-24°C) for all the other steps, it's just not going to be an issue with modern B&W films (color film has its own needs).

And no, temperature differences within that range won't greatly affect stop time or fix time or need compensation - as Richardgb mentioned, complete fixing is 2x the time it takes for the cloudiness of the film to "clear." And as I mentioned, avoid trying to fix at less than 19°C - that'll definitely start to require more time.

[pridbor]

Like the Post initiator I too am very new to Home development, and the above info is very valuable!

I have a follow up question to the statement "The first bath is used until the film clears" made by Richardgb, and that is "how do you know when the film is clear"?

Do you open up at the end of the stop bath to look and then continue if not clear? 

Thanks 

Preben

[Pyrogallol]

No, do not open the tank until the fixer (rapid fix) has had at least a minute to work, a bit longer for non-rapid fixer.

when you open the tank and look at the film you should see the film clear of the milky look of unfixed film. If it still looks milky leave it in the fixer for a few minutes longer, with agitation, or mix some fresh fixer and discard the older. It should then quickly clear.

if you want to see how fixer works take a short piece of undeveloped film, black and white film rather than colour negative, and put it in a small tray with some fixer, in daylight so you can see it, and watch how long it takes to clear. I use that to check my printing paper fixer as you cannot see if darkroom paper has been fixed fully or not in the dish.