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.
Your scans weren't attached, Patrick.
How did the negatives perform, photographically? Do you have a sense of curve shapes yet? I've had nice results with my equipment and techniques with metol-based concoctions lately so this caught my attention.
Thanks again for your energy and expertise in these matters!
My attachments got attached to the end of the superadditivity thread started some time ago by PE. My bad. You can see them there.
Originally Posted by craigclu
I like the results very well. Metol-ascorbate has a little advantage over phenidone-ascorbate in that Metol has more tanning action. The relief effect seems to make edges a little different due to the diffraction. I have done essentially this same thing using phenidone, but cannot dissolve 0.05 moles of it. 0.01 moles, 1.62 grams, of phenidone substituted for the Metol is quite potent, however. Only half the hydroxide is required since phenidone has no attached acid molecule.
Interesting formula, but there seems to be a lot developer relative to the activity! By comparison, I use a version of MC-TEA plus sulfite that has approximately the following amounts in the working solution. It is slower than the developer you describe here, but not in proportion to the amount of developing agent. Without sulfite, this developer does practically nothing.
ascorbic acid 1.9 g (actually C-1000, health-food store version that is about 40 percent less active than pure ascorbic acid)
sodium sulfite 10g
Delta 400 35 ml 75F 14min.
Last edited by psvensson; 06-04-2007 at 02:47 PM. Click to view previous post history.
Hm, looking at all the components in two developers, not just the developing agents, they're not that different. The formula on top is about 40 grams of stuff in a liter of water, mine is 20g. And my development time is probably 70 percent longer.
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It is possible that the difference in pH is enough to stimulate synergism. I have had developers with about the ratio of Metol-ascorbate without sulfite but with carbonate that are very active. Around pH=9 which you should get with borax in place of the TEA you might find you don-t need the sulfite. The research I based my experiment on used 0.05 moles of ascorbic acid at pH=8.7. I have to go now. Will return.
My purpose in these experiments was to get a practical feel for the results I saw in "Theory of the Photographic Process". Sometime I feel that there might be an advantage in a "thick", less active developer over the thin but very active ones we see a lot of now. My idea was one that would be more or less self replenishing. Phenidone would be a better candidate for that because of it lower sensitivity to bromide build up.
The pH is between 9 and 10 according to my test strips, and it won't change much with dilution because there's a lot of borax in there.
I'm still trying to figure out what you have. There may be as little as 4.5 grams of TEA in a liter that is not neutralized by the ascorbic acid and the sulfuric acid on the Metol. I have a table that tells what pH one might expect.
It says 4.5 grams of TEA/100 ml of solution should give a pH about the same as borax. You have only about 1/10 that amount. It would be a good thing to know if the sulfite was acting as sulfite or just as extra alkali. You could try using 10 grams of borax instead of the sulfite to see what happens.
Another point is that the curve from Mees & James shows that the effect of either ascorbic acid or sodium sulfite increases as mole fraction rises to about 0.05, then levels off with further increase. Thus 10 g/l sulfite is well above that point while 1.9 g/l even of full strength ascorbic acid is far below. If you were to bring the ascorbic acid up to 8.8 g/l (as an ascorbate, of course) you might see the activity increase without sulfite. However. I don't think you have quite enough pH without the sulfite. It should be about 9.
I have a feeling that it is the molar concentration of either the ascorbic acid or the sulfite that counts, not the ratio of either to the Metol, as long as the pH is right.
Yes, I'll try adding more TEA instead of sulfite and see where that gets me. I concocted this mixture to save on TEA, the only ingredient I can't obtain close by.