question for chemists...

[David Lyga]

I have wondered for some time whether or not this is true: When you add BOTH sodium carbonate and sodium bicarbonate (baking soda) to a developer, is the accelerator then more stable?

I swear that the baking soda makes for a smoother development. Baking soda slightly reduces the accelerating effect, but only slightly, when added in the same amount as the carbonate. Is my 'stability claim' completely unfounded? - David Lyga

 

[David Lyga]

You are correct: I was thinking of sodium bicarbonate but my fingers typed bisulfite (aided by a faulty mind). Baking soda is what I meant: sodium bicarbonate. I have corrected the original post. - David Lyga

 

[Gerald C Koch]

Sodium carbonate and sodium bicarbonate will form a buffer system. As such the system will resist small amounts of acid or alkali. However, what is meant by the term smoother development?

 

[David Lyga]

Gerald, I did not know how to express what I felt. (It is as simple as that.) Not able to quantify, I strove to personify!

There was something about that bicarbonate developer that I knew was better. "Smoother" came about this way: oftentimes, in full room light, I will immerse a sliver of film or paper and watch how density builds. On developers that have the baking soda, I noticed that the density built more evenly. Sufficient density resulted from each, but it was more satisfying to watch the 'smoother' build up with the sodium bicarbonate-incorporated developer.

Gerald, you said what I was seeking. Thank you.

May I also ask this? Does SB provide any help with limiting age-fog since it does slow development somewhat? - David Lyga

 

[cliveh]

Gerald, I did not know how to express what I felt. (It is as simple as that.) Not able to quantify, I strove to personify!

There was something about that bicarbonate developer that I knew was better. "Smoother" came about this way: oftentimes, in full room light, I will immerse a sliver of film or paper and watch how density builds. On developers that have the baking soda, I noticed that the density built more evenly. Sufficient density resulted from each, but it was more satisfying to watch the 'smoother' build up with the sodium bicarbonate-incorporated developer.

Gerald, you said what I was seeking. Thank you.

May I also ask this? Does SB provide any help with limiting age-fog since it does slow development somewhat? - David Lyga

Complete tosh. To control the pH of a developer sodium carbonate is the alkali commonly employed. Sodium bicarbonate is useless as the alkali in a developer.

 

[removed account4]

hi david

im no chemist and i don't play one on tv, but
sodium bicarbonate and sodium carbonate are similar
AND you can actually bake SBC, force moisture out of it
and create SC ... SO
i would imagine SC would be more active, and SBC be less active
but do similar things ...

YMMV

tosh? is that PETER TOSH ?
saw him live years ago, amazing show, amazing presence ire, mon!

 

[Gerald C Koch]

The bicarbonate ion acts as a weak restrainer. This property was used by Geoffrey Crawley for one of his FX series developers. He was insistent that crystalline potassium carbonate (the sesquihydrate) be used rather than the anhydrous form. The sesquihydrate contains a small amount of bicarbonate as an impurity. The bicarbonate is necessary for the proper working of the developer. In the early days of photography many developers were made using sodium carbonate and sodium bisulfite. This produced sulfite and bicarbonate ions. These developers seemed to work better than those made from carbonate and sulfite.

 

[Europan]

Friends, you have one eye closed.

Talking developer formulae is incomplete without a view of the film.
What is it about the film?

The photographic layers consist of gelatine and that behaves in different manners according to the solution’s pH value. It swells in alkaline solution, the more rapidly and further the more pH is above 7. Buffering the alkali is one of a bunch of measures to steer the so-called development.

There are big differences between old-fashioned thick-layer black-and-white films, especially with non-hardened gelatins, and modern all-hardened films with thin layers such as the color/chrome stocks or Gigabitfilm. That’s why there are so many formulae with sometimes only minor differences.

I think it is wise to observe a plate, a film or a paper with an eye on the soup and one on the bone. We can give more salt to the water but the bone is the deer.

 

[pdeeh]

I think it is wise to observe a plate, a film or a paper with an eye on the soup and one on the bone. We can give more salt to the water but the bone is the deer.

i can't tell you how much pleasure this sentence gives me

 

[cliveh]

The bicarbonate ion acts as a weak restrainer. This property was used by Geoffrey Crawley for one of his FX series developers. He was insistent that crystalline potassium carbonate (the sesquihydrate) be used rather than the anhydrous form. The sesquihydrate contains a small amount of bicarbonate as an impurity. The bicarbonate is necessary for the proper working of the developer. In the early days of photography many developers were made using sodium carbonate and sodium bisulfite. This produced sulfite and bicarbonate ions. These developers seemed to work better than those made from carbonate and sulfite.

If you want a restrainer, I would suggest Potassium bromide would be a better choice.

 

[David Lyga]

jnanian: I know that bicarbonate is NOT an accelerator. But I wanted to know if, somehow (as my 'instinct' seemed to guide me) that bicarbonate made the carbonate work better and with more stability. Gerald Koch indicates that this is true and I thank him for this information.

Again, I do not really know why I 'knew' this already, as I am not a chemist and had no theoretical foundation or basis for this claim; I just 'felt' that it was better to have the bicarbonate present. This forum is a font of information and insight.

NB: cliveh: I regularly use either potassium bromide or benzotriazole as restrainers. I simply wanted to know if, ALSO, sodium bicarbonate had at least some restraining action whereby the lesser densities would be attacked quicker than the higher densities would be. - David Lyga

 

[Gerald C Koch]

If you want a restrainer, I would suggest Potassium bromide would be a better choice.

Many chemicals can act as restrainers in the photographic process. Commonly potassium/sodium bromide, benzotriazole and potassium iodide are used. Each may have a different effect and/or use. Potassium bromide and benzotriazole will change the image tone in a print. Crowley appeared to think that bicarbonate was desired for his developer. He did not give a specific reason for his choice.

Development is a very complex process and some chemicals have unexpected effects. An individual chemical may serve more than one purpose. There is nothing wrong with this and indeed it may be desirable. It has long been observed that borates improve a developer containing hydroquinone. There is less fog produced. After study it was found that one of the oxidation products of hydroquinone hydroxyhydroquinone is a very active developing agent. Borates complex with quinols where two of the hydroxyl groups are in the ortho (adjacent) position severely limiting their photographic activity. In this respect borates act as restrainers in the given case but not in general. This is why borates cannot be used as accelerators for catechol based developers.

 

[miha]

What would be in an alkaline stop bath then for it to work?

 

[cliveh]

What would be in an alkaline stop bath then for it to work?

Miha, I think you are moving into the realm of Pyro developers.

 

[cliveh]

Many chemicals can act as restrainers in the photographic process. Commonly potassium/sodium bromide, benzotriazole and potassium iodide are used. Each may have a different effect and/or use. Potassium bromide and benzotriazole will change the image tone in a print. Crowley appeared to think that bicarbonate was desired for his developer. He did not give a specific reason for his choice.

Development is a very complex process and some chemicals have unexpected effects. An individual chemical may serve more than one purpose. There is nothing wrong with this and indeed it may be desirable. It has long been observed that borates improve a developer containing hydroquinone. There is less fog produced. After study it was found that one of the oxidation products of hydroquinone hydroxyhydroquinone is a very active developing agent. Borates complex with quinols where two of the hydroxyl groups are in the ortho (adjacent) position severely limiting their photographic activity. In this respect borates act as restrainers in the given case but not in general. This is why borates cannot be used as accelerators for catechol based developers.

Yes, so why do most commercial developers use potassium bromide and not bicarbonate?

 

[miha]

Miha, I think you are moving into the realm of Pyro developers.

Nope, I'm staying with PQ formulas, but I'm interested in how an alkaline stop stops the developing process.

 

[cliveh]

Nope, I'm staying with PQ formulas, but I'm interested in how an alkaline stop stops the developing process.

Because it's used after an acidic developer.

 

[miha]

Hopefully not

 

[Rudeofus]

Yes, so why do most commercial developers use potassium bromide and not bicarbonate?

There are two ways to prevent fog: add something that binds to Silver ions (commonly called restrainers, like Benzotriazole, Bromide, Iodide), or lower pH. Both will do the job but have slightly different effects.

Nope, I'm staying with PQ formulas, but I'm interested in how an alkaline stop stops the developing process.

From my above statement you can derive easily how to formulate a stop bath: either load it with restrainer, or achieve a low pH. Most common stop bath formulas use low pH, but if you want an alkaline stop bath you need to go the first route.

Because it's used after an acidic developer.

Most film developer compounds become more active if you raise pH, even the one that is commonly used at low pH (Amidol). A plain alkali will therefore not stop any film developer I know of, unless you load it with restrainer, as mentioned above.


@David Lyga: When a Silver ion gets developed, the reaction products are slightly acidic and inhibit development. High acutance developers use this very effect to achieve higher perceived sharpness. In your case you see that development starts, then somehow stops, only to pick up speed again after more alkali has diffused into the gelatin. If you form a strong Carbonate/Bicarbonate buffer, the acidic byproducts from development won't affect pH that much. As a result development process will appear "smoother" as you called it.

 

[Gerald C Koch]

Yes, so why do most commercial developers use potassium bromide and not bicarbonate?

Because as I said bicarbonate is a weak restrainer, some would say a very weak one but in certain circumstances all that is needed.

 

[cliveh]

Because as I said bicarbonate is a weak restrainer, some would say a very weak one but in certain circumstances that is all you need.

And what circumstances would they be?

 

[Rudeofus]

Because as I said bicarbonate is a weak restrainer, some would say a very weak one but in certain circumstances all that is needed.

If you add Bicarbonate to Xtol, it won't act as restrainer, quite to the contrary, it will increase its activity. Adding it to Dektol, on the other side, will likely reduce developer activity.

In other words, it depends on the pH of your developer whether Bicarbonate acts as restrainer or not.

 

[Gerald C Koch]

And what circumstances would they be?

I don't know. Ask Geoffrey Crowley, he developed the formula - oops he's dead.

 

[Gerald C Koch]

If you add Bicarbonate to Xtol, it won't act as restrainer, quite to the contrary, it will increase its activity. Adding it to Dektol, on the other side, will likely reduce developer activity.

In other words, it depends on the pH of your developer whether Bicarbonate acts as restrainer or not.

You are equating the action of a restrainer with a change in pH. The amount of bicarbonate in Crowley's formula is quite small. The amount of bicarbonate in potassium carbonate sesquihydrate usually given as 1.5%.

 

[nworth]

When bicarbonate and carbonate form a buffer system, the pH (alkalinity) is somewhat less than for carbonate alone. That is probably the reason for the "smoother" development. Yes, buffered developers are a bit more stable than unbuffered ones.