Alkali stop and fix - really visible results?

Usagi · Jul 24, 2007

Hi,

Some sources say that with alkali stop and alkali fix, the highlights will be better.
But is that only in theory or in practice?
I wonder this, because many of great photographers doesn't mention any of use of alkali process.

Currently I have alkali stop and alkali fix, but I haven't done any comparisons with results.

MichaelMadio · Jul 24, 2007

I seriously doubt any difference in highlights ... at least there's none that I can see. I use alkaline fix as I find it convenient.

Michel Hardy-Vallée · Jul 24, 2007

Alkali stop? What formula do you use? I haven't seen much about alkali stop baths.

The all-alkali chain is mainly to give you a better washing of the chemicals (thiosulfates) from the fixer.

I can see some theoretical truth in the highlights argument. Basically, ammonium thiosulfate in acid solution (rapid fixer) is a reducer. If you fix a print for too long, the fixer will attack the solid silver of the print. Given that the highlights are where there is the least density, highlights will whiteout first before the shadows have any visible density loss.

In alkaline solution, ammonium thiosulfate does not have this property. Therefore, an alkaline fixer theoretically prevents highlight density loss.

I've never tested the time necessary for rapid fixer to start attacking the highlights, so this theoretical advantage may or may not be a practical advantage. The reduced washing time is probably a more directly useful advantage.

David A. Goldfarb · Jul 25, 2007

I suspect the context is relevant.

One of the attractions of staining developers for negative film is better highlight detail, and with a staining developer, an alkaline fix will preserve stain density better than an acid fix, and with an alkaline fix, one shouldn't use an acid stop (or at least not a strong one), or it will weaken the fix.

So if you use a pyro developer for film, an alkaline fix will give you better highlights than an acid fix, but that is not because of something the fixer does, but rather what the developer does and the fixer doesn't do.

AgX · Jul 25, 2007

mhv said:
Basically, ammonium thiosulfate in acid solution (rapid fixer) is a reducer. If you fix a print for too long, the fixer will attack the solid silver of the print. Given that the highlights are where there is the least density, highlights will whiteout first before the shadows have any visible density loss.

How could a reducing agent harm the highlights, as the halides already have been reduced by the developing agent to metallic silver?

Michel Hardy-Vallée · Jul 25, 2007

AgX said:
How could a reducing agent harm the highlights, as the halides already have been reduced by the developing agent to metallic silver?

Sorry, bad vocabulary. I meant "reducer" as in "Farmer's reducer."

Lowell Huff · Jul 25, 2007

Alk or acid fix

Lacking any scientific evidence to the contrary, the difference between acid and alkalyn fixers is anicdotal. It is the amount of thiosulfate in the solution that determines the capacity, not the pH. The ammonia attached to the thio gives the speed over Sodium thio. The big advantage for acid fixers is that they can be used as a "stop-fix", no stop bath required.

karavelov · Jul 25, 2007

Yes, I have also experience of reduced highlights with overfixing in acid rapid fixer. This will be even worse if you use staining developer. Do not use acid stop but plain water if you use alkaline fixer - you risk to find a lot of pinholes in the film.

Neanderman · Jul 25, 2007

Bleaching of highlights from overfixing is much more likely to happen on a print than on a negative, due to the more finely divided silver filaments in prints.

Ed

AgX · Jul 25, 2007

reducer

Sorry mhv,

I mixed up reducer with an agent with redox potential. I was just switching from German (Reduktionsmittel=agent w. redox potential) to English with some negliance.
Writing in parallel in several languages needs more attentiveness...

dancqu · Jul 25, 2007

AgX said:
How could a reducing agent harm the highlights,
as the halides already have been reduced by the
developing agent to metallic silver?

Potassium ferricyanide is not a reducer it is an oxidizer.
As mentioned above the elemental silver is in it's most
reduced state. Ferricyanide converts elemental silver
to silver ferrOcyanide. The latter is insoluble so the
integrity of the image is maintained. Farmer's first
oxidizes the silver.

Add some bromide to a ferricyanide solution. Due
to the greater insolubility of silver bromide over that
of silver ferrocyanide the silver will convert to silver
bromide. If added to solution, chloride, iodide and
who knows how many other interesting insoluble
silver salts may be the result. Dan

Michel Hardy-Vallée · Jul 25, 2007

AgX said:
Sorry mhv,

I mixed up reducer with an agent with redox potential. I was just switching from German (Reduktionsmittel=agent w. redox potential) to English with some negliance.
Writing in parallel in several languages needs more attentiveness...

I know, I had once the exact same reaction when I read some photochemistry stuff. In French we use "oxydoreduction" for the chemical reactions involving electrical charges and ions.

Usagi · Aug 9, 2007

mhv said:
Alkali stop? What formula do you use? I haven't seen much about alkali stop baths.

The all-alkali chain is mainly to give you a better washing of the chemicals (thiosulfates) from the fixer.

Hi,

I use Alkali-Stop and Alkali-Fix from http://www.monochromephotography.com

Michel Hardy-Vallée · Aug 9, 2007

Usagi said:
Hi,

I use Alkali-Stop and Alkali-Fix from http://www.monochromephotography.com

Thanks, I'm really surprised (and interested) to see that there is a commercially produced alkaline stop bath. In Anchell & Troop, they still listed the technology as experimental.

What's been your experience with it, is it reliable? Have you tried it mostly on film or paper?

john_s · Aug 10, 2007

I use non-acidic fixer because it smells far less than the traditional somewhat acidic fixer. Also, it's far cheaper*, allowing me to replenish more and keep my fixer in best condition.

* I used to use Agfa FX-Universal (pH=7.5) but now I've had to revert to Kodak Flexicolor Fixer (pH=6.5approx). Half the price of "black and white" fixer!

Usagi · Aug 10, 2007

mhv said:
Thanks, I'm really surprised (and interested) to see that there is a commercially produced alkaline stop bath. In Anchell & Troop, they still listed the technology as experimental.

What's been your experience with it, is it reliable? Have you tried it mostly on film or paper?

I have tried it only with films. Seems to work fine, but I haven't done any tests of fixing quality.

Dave Miller · Aug 10, 2007

Usagi said:
Hi,

I use Alkali-Stop and Alkali-Fix from http://www.monochromephotography.com

I use the same products, and have for a couple of years without problem. I'm just as happy using a water wash in place of the Alkali-stop.

Roger Hicks · Aug 10, 2007

Dave Miller said:
I use the same products, and have for a couple of years without problem. I'm just as happy using a water wash in place of the Alkali-stop.

How does Alkali-Stop work? What does (can) it do that water doesn't? I'm puzzled...

Dave Miller · Aug 10, 2007

Roger Hicks said:
How does Alkali-Stop work? What does (can) it do that water doesn't? I'm puzzled...

It dosn't do anything water cannot do, it just does it a little quicker. Just as an acid stop bath can be replaced by water baths.

Tom Hoskinson · Aug 10, 2007

Lowell Huff said:
Lacking any scientific evidence to the contrary, the difference between acid and alkalyn fixers is anicdotal. It is the amount of thiosulfate in the solution that determines the capacity, not the pH. The ammonia attached to the thio gives the speed over Sodium thio. The big advantage for acid fixers is that they can be used as a "stop-fix", no stop bath required.

On the contrary, There is a lot of well documented scientific evidence for the advantages of alkaline and neutral fixers that contain ammonium ion: Not only anecdotal.

See Grant Haist's Modern Photographic Processing, Volume 1, Wiley Interscience, 1979; pages 633 - 65, also see pages 588 - 592

dancqu · Aug 11, 2007

Roger Hicks said:
How does Alkali-Stop work? What does (can) it do
that water doesn't? I'm puzzled...

The link supplied by USAGI provides some explanation.
They link their sweet stop to staining developers. In and
of itself an alkaline stop is not a stop at all. In fact it might
be considered the B bath of a divided developer. If only
a little alkaline and well buffered that stop will dilute
and neutralize the developer present.

Apart from ph itself something else may make a stop of
a ph sweet stop; the rapid oxidation of the developing
agent by some mild oxidizer. Off hand I've no idea
what that oxidizer might be. Dan

nworth · Aug 11, 2007

David A. Goldfarb said:
I suspect the context is relevant.

One of the attractions of staining developers for negative film is better highlight detail, and with a staining developer, an alkaline fix will preserve stain density better than an acid fix, and with an alkaline fix, one shouldn't use an acid stop (or at least not a strong one), or it will weaken the fix.

So if you use a pyro developer for film, an alkaline fix will give you better highlights than an acid fix, but that is not because of something the fixer does, but rather what the developer does and the fixer doesn't do.

Dave is giving you the right information here. If you use a pyro or pyrocatechin based developer (e.g. PMK, Pyrocat-HD, Rolo-Pyro, 510-Pyro, ABC, etc.), you need to avoid acid conditions to maintain maximum stain. With other developers, it doesn't matter. There is no such thing as an alkaline stop bath. Instead of a stop bath, you should use a plain water rinse to stop the development action with these developers. (I usually flush the tank twice with water instead of using a stop bath with any developer.) You can use either a neutral or alkaline fix with these developers. You can even use a slightly acid fix without doing much harm. One advantage to an alkaline fix like TF-4 is that it washes out much faster and better than an acid fix like Kodak Fixer.

Dave Miller · Aug 12, 2007

nworth said:
"snip" There is no such thing as an alkaline stop bath.

Strange that, since I've got several bottle of the stuff in my darkroom:confused:

Michel Hardy-Vallée · Aug 12, 2007

In 1998, Anchell & Troop were saying the following about alkaline stop baths:

Film Development Cookbook said:
Alkaline stop baths have not yet gone beyond the experimental stage. The approach that has been taken is to use a high concentration of an antifoggant, such as 5-10% potassium bromide, 0.5-1% benzotriazole, or 0.05%-0.1% 1-phenyl-5-mercaptotetrazole. Sodium sulfite should be added as a preservative to help prevent swelling and oxidation staining. Between 2% and 5% is a suitable amount. An alkali buffering system may be used to keep pH within the desired range, which will probably be between 8.5 and 10. A combination of sodium metaborate and sodium bisulfite would be suitable for trial.

So what would be the effect on developers of a high concentration of antifoggants? Rapid oxidation of the reducing agents?

Ole · Aug 12, 2007

mhv said:
So what would be the effect on developers of a high concentration of antifoggants? Rapid oxidation of the reducing agents?

More like protection of remaining undeveloped silver halides from developing agents than any breakdown of the developer.

Borate (borax or metaborate) is also rumored to have "stopping" effects on some developers, mostly pyrocatechol.

Alkali stop and fix - really visible results?

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