Experiments with Metol and ascorbic acid.
The factors affecting developer activity are temperature, pH,
concentration, products of aerial oxidation, products of silver halide
reduction, and the orientations of the heavenly bodies.
According to some experimental results reported in "The Theory of the
Photographic Process" as little as 0.05 moles (6.3 grams) of sodium sulfite in
a liter of Metol developer will double the rate of development that is
obtained when no sulfite is present, pH being held at 8.7 in both cases.
It is explained that oxidation products of Metol restrain development, and
that sulfite counteracts these products by forming the sulfonate.
Ascorbic acid will do the same degree of acceleration without sulfite, also at pH 8.7. In this case the oxidized Metol is reduced back to its original form. The ascorbate is itself oxidized and pH is decreased in the process. The decrease in amount of active Metol in the one case or the decrease of pH in the other may not cause much difference in capacity and storage longevity between a Metol-sulfite and a metol-ascorbate developer. However, it would seem that a well buffered working solution might tip the balance in favor of the ascorbate.
I will explore first a 0.05 molar concentration of Metol, which is
approximately that of D-23, together with a 0.05 molar concentration of
ascorbic acid. It remains to formulate the alkali needed to make the pH less
than that at which an ascorbate becomes a developer and great enough to ensure activity of Metol.
I calculate that 0.1 moles of sodium hydroxide will neutralize the 0.05
moles of sulfuric acid attached to the Metol base plus the 0.05 moles of
ascorbic acid, leaving 0.05 moles each of sodium sulfate and 4-(methyl-
amino)phenol and 0.05 moles of sodium ascorbate. The net pH thus far is still
not alkaline enough to develop film in a reasonable time, nor does it have the
necessary buffering action to keep the pH from going lower yet. A few grams of borax should bring the pH up to about 9.2 but even 20 grams will have little
more effect on pH and should give a cushion against reduction of pH during
The resulting recipe is:
Ascorbic acid.....8.8 g
Sodium hydroxide..4 g
Water to 1 liter.
The concentration of Metol is about 13% greater than in D-23 and the
concentration of sodium sulfite is nil.
The pH of this mixture, which I measure with test strips to be about 9, is
below that at which the ascorbate is a developer of any consequence. The
initial activity of the mixture is about that which could have been obtained
with sulfite in place of the ascorbate, so it does not seem that synergism
between Metol and ascorbate is the explanation.
The ratio of borax to caustic in this formula is quite close to the
effective ratio in sodium metaborate. 14.5 grams of sodium hydroxide and 69
grams of borax in a liter make a solution that is often used as a substitute
for 10% sodium metaborate. 276 ml of such a solution, or 27.6 grams of Kodalk if you prefer, will contain the equivalent of 4 grams of sodium hydroxide and about 20 grams of borax. It may be easier to get sodium metaborate than sodium hydroxide through the UPS. The recipe then becomes:
Ascorbic acid......8.8 g
Sodium metaborate..27.6 g or 276 ml of 10% sodium metaborate solution.
Water to 1 liter.
All ingredients are quickly dissolved in room temperature water. HP5+
developed for 8 minutes at 68 F gives normal contrast, showing that the
solution could be diluted. In fact, diluting with an equal part of water
increased development time by only 25%, probably because the pH of this
solution does not change much with dilution. 125 ml diluted with 125 ml of
water did a 36 exposure roll of HP5+ to normal contrast in 10 minutes, which
means of course that a liter of the above formula will do 16 standard rolls
without reuse. As a matter of interest, twice the above recipe can be squeezed into one liter.
By the way, don't be confused by the fact that there exist 4 mol and 8 mol
metaborates. A gram of one has the same number of atoms of sodium, boron,
oxygen and hydrogen as a gram of the other. At 53.6 C, without losing any
water, Na2B2O4.8H2O becomes NaBO2.4H2O which is stable to 105 C. In other words, the distinction between 4 mol and 8 mol sodium metaborate is academic, not practical when we specify solution strength in terms of weight per unit volume. You may see this for yourself at www.borax.com.
I am attaching a scan of a 10x print from FP4+ developed 8 minutes, 68 F. This is not of very high resolution, but may serve to illustrate gradations. I have also attached a higher resolution scan of a small part of the same print. If you print the high res. scan to 6x9 inches, you will see about a 50X magnification of that part. I have no idea how these will show up, but you can imagine that the originals are better.
As it turned out, the attachments showed up at the end of the thread on superadditivity started by PE. My fault.
Last edited by gainer; 06-03-2007 at 10:23 AM. Click to view previous post history.
While you are about it, add 8.8 grams of ascorbic acid and 6.6 ml of TEA to the liter of working solution without sulfite and check the activity.
Meanwhle, I cut the Metol to 0.01 moles /liter (3.44 grams), used 8.8 grams/l of ascorbic acid and 16.6 grams of sodium metaborate, and the activity is almost what it was with 0.05 moles of Metol.
I'm ashamed to say it, but 8.5 grams of Metol are 0.025 moles, although the resulting solution contains 0.05 moles of 4(methyl-amino)phenol after the sulfuric acid has been separated. The 3.44 grams actually make 0.02 moles of 4(methyl-amino)phenol. By some bit of luck, or maybe my brain was working then, I got the amount of hydroxide right so the solution pH is as close to 9 as my pH strips will tell me.
I found that the developer using phenidone gives about 1 f-stop more film speed, although I used the box speed with the Metol version and got good shadow detail. I guess the phenidone version would be good for unavailable light.
I'm not entirely sure about that difference in speed. A difference in fog density can look like a difference in speed at first glance.
This is copied from the post on edge effects. Mix 1/2 teaspoon of Phenidone with a little isopropyl rubbing alcohol to make it easier to dissolve in water. Mix a couple of ounces of water, 2 teaspoons of ascorbic acid powder and 1 teaspoon of sodium bicarbonate and stir til the effervescence subsides. Warm it slightly to get more CO2 out. Add this mixture, the Phenidone, two teaspoons of borax and enough cold water to make 1 liter. Use it full strength or diluted as you would use D-76. At full strength it can be reused for at least 8 36 exp. or 8x10 films. All the teaspoon measures are levelled standard cooking measuring spoons.
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Now let's play with p-aminophenol.
Paraminophenol is not very soluble in water. The potassium aminophenolate is quite soluble and a very active developer. Before we knew it as the proprietary Rodinal, Hurter and Driffield referred to a developing agent named rodinal, which I think might have been potassium aminophenolate. We can make a 0.05 molar solution of this rodinal from 0.05 moles of potassium hydroxide and 0.05 moles of p-aminophenol base, add to it 0.05 moles of ascorbic acid and another 0.05 moles of sodium or potassium hydroxide and some borax and end up with a kinder and gentler Rodinal expedient. Maybe.
This recipe is:
5.45 grams of p-aminophenol base
8.8 grams ascorbic acid
28 grams of sodium metaborate
Water to 1 liter.
( the 28 grams of metaborate includes the equivalent of 4 grams of sodium hydroxide and a bunch of borax.
I doubt that you will want to use this stuff full strength.
You can make a 2-part concentrated developer as follows.
Dissolve 22 grams p-aminophenol base and 35.2 grams ascorbic or erythorbic acid in about 400 ml propylene glycol. Add glycol to bring volume to 500 ml. This is solution A.
Dissolve 110 grams of sodium metaborate in water to make 500 ml. This is solution B. If you do not have metaborate, use 16 grams of sodium hydroxide or 22 grams of potassium hydroxide plus 76 grams of borax
Mix equal parts of A and B in water. A typical dilution would be 1:1:25. A typical development time for FP4+ would be 8 minutes at 70 F.
If the ascorbic acid were regenerated, then this would be an electron transport developer. Unfortunately, if the other agent is consumed, it is not an ET developer. It is superadditive though.
Say what? I am confused. That's a normal state of mind for me, but I need education. I think the ascorbic acid is consumed and the other agent is not, at least until the ascorbic acid is no longer able to function as a a reducer of the other agent. That seemed to be the conclusion reached by the experiment reported in Mees & James. What sort of concoction would keep both agents from being consumed? Don't give away any secrets if that is what this is about.
Originally Posted by Photo Engineer
It appears that you have said that if either agent is consumed, it is not an ET developer. I don't recall seeking an ET developer. I've gotta go eat. I'll mull it over and try to figure out what you said.
Patrick; Any biochemistry text will draw chemical reactions with circular arrows for each reactant. Things keep cycling each other. With an ET developer, it can either recycle both ingredients or have one 'pump' the other in activity. Both types can be ET, but the former, with total cycling is distinctive enough to be clearly an ET developer. The latter requires many tests to show if it is an ET developer. It may or may not be. It may just be ordinary superadditivity.
The clue in this in the latter case is if either agent is virtually inactive alone even at high concentrations. Placing a large amount of the most inactive into the developer, and a tiny amount of the other (which is recycled) will give a very active, long lived developer with high capacity. The one at high concentration and with low activity is being used up to regenerate the small amount of the other agent.
Now I feel better. That is what I thought I was doing, although I agree that 0.05 moles of p-aminophenol is probably not a relatively small amount for a working solution considering that Rodinal has less than 1/5 that much in a 1+50 working solution. The pH of Rodinal is quite high, while my experimental stuff is between 9 and 10, probably that of a borax solution.
Originally Posted by Photo Engineer
The working solution I use with the concentrate diluted 1+1+25 has only about 0.8 grams/liter.
I should test to see how little I can use.
Another factor is that if the developer contains only sodium ascorbate at the pH of borax, we will wait all day for something to happen.