Assuming fixer is going to be used just once then discarded or it is going to be the last time this particular fixer is being used, are there any scare stories or even actual facts suggesting that it's not a good idea to pour out the developer then pour in the fixer without a stop bath or water bath? I'm assuming acid fixer and film, not paper.
You run a much higher risk of dichroic fog staining the emulsion Steve. If the fixers being used one-shot it's also likely to be made up at a lower concentration raising the risk further.
So assuming the same diffusion takes place with a water rinse compared to a stop bath then all's equal. In practice the lower pH of an acid stop bath should reduce the rate of diffusion as it reduces the swelling of the emulsion.
Originally Posted by Photo Engineer
If an emulsion is placed in stop bath then we assume development stops, but if it's then placed back in an alkali solution some further development takes place dependant on the residual retained developing agents.
It's good agitation whether a water rinse or stop-bath that's most important.
Forgive me, but all this reminds me of the old story of the group of philosophers aguing about how many teeth a horse has. Finally, one of the philosophers suggests that they find a horse and actually count the number of teeth. The others turn on him and beat him severely.
Nowhere in all these comments is there any citation of an actual independent scientific study. I'm sure there must be a least one.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
The reason I asked is because I have done this a couple of times although I always mix the fixer up to normal strength.
Originally Posted by Ian Grant
I have not seen a problem and was not expecting there to be one but thought it was worth asking the question.
I suppose my assumption was that as the fix is acidic then it should stop development just like a stop bath only more so. Another assumption here is that the fixer is more acidic than stop. I have never tested either and don't intend to.
I think there is a good mix of trying out different things and listening to the wise advice of others in this thread. I think the trying of different methods is important even if it goes against the wise advice because if we never tried anything out we would never learn anything new.
Originally Posted by alanrockwood
I suggest no such thing as a unipolar diffusion. I am suggesting neutralization!
The coating is alkaline with enough hydroxide ions present to achieve the desired pH of the developer. The protons move in to meet the hydroxide ions and they reach the bottom of the coating in a rush so fast that it is difficult to measure.
Meanwhile the Acetate ion and the Sodium ion lazily diffuse towards each other. So, neutralization is virtually instantaneous, but equillibration is much slower.
That is what I am describing. The rapid movement of Hydrogen ion to neutralize the hydroxide ions present in the coating. At the same time, excess Hydrogen ion is protonating the Metol.
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I use a stop bath for color paper to promote uniformity and remove the developing agent. The developing agent (CD3) is not very soluble. The CD4 used in C41 is much more soluble and can be removed by the bleach which is more acidic than the RA blix. The same is true of E6 which uses a more acidic bleach and a slightly acidic reversal bath.
Originally Posted by srs5694
Originally Posted by Gerald C Koch
There are none published AFAIK. I have published on this several times in internal EK reports. The color problem was so severe that Ektacolor 30 was almost taken off the market for a short period in 1970, but we just added the stop.
You see, the original EP3 process was Develop, Blix, Wash, Stab. Kodak wanted a 2 step EP2 process so they got rid of the Stab at the last minute which was a pH 4.5 Citric Acid bath. The image stability tests showed no problem, but in real life the prints were turning pink after about 6 months. The bulk of our tests had been done with the Stabilzer, and we saw no problem removing it.
In our tests we ran a 2 week wet and dry oven test and saw no problem, but then over that Christmas when the problem was first seen in the trade we tested the prints daily and after about 2 -3 days we saw a pink stain and then the stain vanished. Prints affected this way then browned in a few years and began turning red.
Adding the stop bath fixed 2 problems. It extracted the CD3 from the coating thus eliminating the dye stability problem and it gave better uniformity in the Jobo processors which were just becoming popular at that time.
Why get rid of the stabilizer at the last minute? Well, it was an extra solution and all of the stabilizing agents were in the coating for the first time. The effect of the final stabilzer was minimal (or so we thought). So, it was deemed that EP2 was the thing to go with. Moral of the story - test many ways and don't make last minute changes!
This was my first introduction into the definite merits of the Stop bath. And, just to be clear, I was only one worker on the project and only one of the workers on the solution. Others made as much or more contribution to fixing this than I did.
Mason indicates that a water wash is sufficient (p201) - Ron you have the same edition I think, there's not a single reference cited.
He goes on to say that a stop bath or wash is superfluous with a well buffered acid fixer, he usually references the Hypam formula ph 5.2-5.4, in other parts of the book as it was Ilford's main fixer from the 50's to today.
He's saying that a wash or stop bath cuts developer carry over, and that a stop bath does arrest development faster and helps prolong the life of the fixer. That must have been Kodak's view at that time (mid 70's) as well.
Yes, Ian, he does, but he also goes on to say that if you use an alum hardener in your fix (as in KRLF), then you can get a precipitate of Aluminum Hydroxide due to the alkalinity carried over. He also restricts this to acidic fixes. There is no mention of neutral or alkaline fixes which are quite popular today. So, his statement is, on the face of it, very very narrowly confined to acidic, non hardening fixers.
But PE, if the hydrogen ions diffuse very fast, with the other ions diffusing very slowly, it is the very definition of unipolar diffusion.
Originally Posted by Photo Engineer
You simply cannot have ions of a certain charge (such as hydrogen ions) being transported without having a very nearly equal amount of a combination of 1) charge of opposite polarity transported in the same direction (the counter ion, such as acetate ion) or 2) charge of the same polarity transported in the opposite direction (such as sodium ions). This is well known physical chemistry.
Therefore, you simply cannot have a nearly instantaneous inrush of hydrogen ions unless it is balanced by either a virtually equal inrush of counter ions or an outrush of ions of the same charge or some combination of the two processes.
As for hydroxide ions, if they are diffusing in the opposite direction of the hydrogen ions then it simply compounds the problem of maintaining local charge balance.
As an interesting aside, a lot of people don't realize the enormous power of electrical repulsion when a charge imbalance is very large. Just for the heck of it try calculating the electrostatic energy of a mole of charge evenly distributed in a sphere of one liter volume. Believe me, you wouldn't want to be standing even a few miles from it as the whole thing explodes from the pent up energy.