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 11:23 AM. Click to view previous post history.
If there's any dye left after fixing, fix some more. Some films have a faintly blue base IIRC, but I haven't encountered any lately.
There's no dye in these formulas like catechol, hydroquinone or pyrogallol. The brown that p-aminophenol turns, as in Rodinal, is not to my knowledge fixed in film emulsion or attached to the image. It often happens with low sulfite developers that the developer solution turns the color of the film's antihalation dye.
Patrick, Assume the film is 320TXP, here are a few questions...
1) If I don't prewash (not just pre-wet) the film, the metol-c dev turns deep, dark blue-purple. Can I re-use it?
2) why is D-23 (for example) almost clear after developing even multiple sheets of film (TXP) while the metol-C developer contemplated here is not? Where does the color go with D-23?
D-23 contains a lot of sodium sulfite which bleaches the dye by design. Its parts are still there in the solution, but arranged by the bleaching so they are colorless. If it worries you, you can add a pinch of sulfite or you can prewash. IIRC, the purple goes away after a while. In any case, I have not found it to be chemically active toward the developer.
OK. Thank you Patrick. I'm going to mix up another batch and not give the funky color a second thought.
So, for the record, I'm using...
9g Ascorbic Acid (vit. C crydtals from heath food store)
distilled water to make 1L
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If any of you are wondering about the possible harm from use of borax of less than Photo grade, whatever that is, I will show you how to reduce impurities in 160 grams of 20 Mule Team or other Technical Grade borax by a factor of at least sixteen at the expense of less than 40 grams of the cheap stuff.
I have recommended making a stock solution of borax and ascorbic acid to which various developing agents can be added to make a complete developer. The stock solution requires about 25 grams of borax per liter.
Weigh out about 200 grams of borax into a bucket big enough to hold 4 liters. Add two liters of ice water. It need not be distilled water at this point, but it will make your conscience feel better if it is water that you would not mind using for D-76. Stir well, let it settle a while and stir it again. This time let it settle while you go watch a TV show or something. What has happened is that only about 40 grams of the borax have dissolved, but all the soluble impurities from the original 200 grams have dissolved. Now decant as much as you can of the clear liquid. You should be able to recover at least 1.9 liters which will contain all but about 5% of the original impurity. That 5% remains in the water that is held by the sediment. You may even be able to squeeze more out by filtering, but do it after decanting. Filtering borax slurry would try the patience of a saint, and I know of no incantation that will speed it up. We shall just have to rely mostly on decantation.
Now the remaining sediment will contain only about 5% of the original soluble impurities in about 80% of the original borax. True, it contains a somewhat higher ratio of insoluble impurities, but need not worry over that. We are not trying to recover powdered borax, but are seeking a solution of borax of certain concentration. Insoluble impurities, by definition, will not dissolve, although the settling time for some may be very long. We will just leave the insoluble stuff behind. So, add 3 liters of water to the sludge in the bucket and stir well. If you do this with water at 17 degrees C (63.6 F) you will saturate the solution at 4 grams/100 grams, using about 120 of the remaining 160 grams.
Again, decant the clear liquid. This time you will get all 3 liters back plus a little because the sludge already was wet from the first solution. The solution is fixed at 4.00% by weight as long as the temperature stays above 63.6 F or 17 C. If it goes below, it will either supercool or precipitate some borax. Measuring the borax will now be done by weighing the solution. Note that neither the water nor the borax had to be measured accurately, but the weight percent is accurately determined by the temperature at which the saturated solution was made, and cannot change once the source (sludge) is no longer present, and as long as the measuring temperature stays above that temperature. 0.1 grams of the solution contains 0.004 grams of borax decahydrate. Thus, measuring the solution to the nearest 1/10 gram is as precise as measuring the powder to the nearest 0.004 grams.
Much of this discussion is of no concern if the solution is only to be used to make the developer's borax-ascorbate stock. Just add another liter of water to the 3 liters of saturated solution you have just made and add 36 grams of ascorbic acid, and you're ready to go.
In a numerical example, suppose 1330 ppm maximum total soluble impurities are guaranteed. Then:
Impurities carried in by 200 grams = 200 * 0.00133 = .266 grams maximum.
2 liters water were added, 1.9 liters liquid decanted. The ratio of impurities dissolved in the output water to those dissolved in the input is 1.9/2 = 0.95. The impurity remaining in the sediment is thus 0.05 * 0.266 = 0.0133 grams. The impurities in the sediment have been reduced by a factor of 20, but only 160 grams remain in the sediment. Thus the total soluble impurities are about 83 ppm, 1/16 of the original.
I found that 20 Mule Team technical grade borax comes in granular or powder form. The specs for the granular say insoluble impurities are <400 ppm. The specs for the powder grade, which is what you get at the supermarket for about 50 cents a pound, show no insoluble particles. The soluble impurities are guaranteed <700 ppm chloride, <600 ppm sulphate and less than 30 ppm iron.
Patrick - if technical grade meets your design specifications, then why waste all your time doing this??
Because you told me technical grade is not good enough for photo work. Further, you said it was not possible for technical grade to have 0 insoluble particles, even though 20 Mule Team Borax from the grocery store is claimed not to be abrasive. Third, because you could not, or ar least did not point to a place where one could find the specs required of Photo Grade borax. At the time I wrote this, I did not know that the specs for technical granular and powder were not the same. Fourth, it takes little time to prepare a gallon or more of borax solution of known weight percentage and of a higher grade than technical, whether it started as granular or powder. Fifth, because there might be some among us who do not know that a solution saturated at a given temperature has a known concentration and can be measured out on a balance more accurately than by weighing the powder directly, even though the temperature is higher that that at which the solution was made.
Originally Posted by Kirk Keyes
First - I said I would try to use a better grade than technical and that I recommend others do as well.
Second - It all depends on your required limit for insoluble particles. If they are sufficiently small enough and there are very few of them, then who cares? You can easily filter a solution through a 0.45 um glass fiber filter and what gets through would be of no consequence, as they would remain suspended in the solution.
Third - I'm still working on that one.
Fourth - OK - it's still extra work to make the gallon.
Fifth - Your're saying that if I weigh a gram of liguid it is more precise than weighing a gram of solid? Please explain. The precision of my balance or scale is still the same. And if I go your method, then I have to trust that I have truely made a saturated solution. If I weigh the dry chemical, then I KNOW that I have exactly what I wieghed. At least to the accuracy of my balance or scale.
You're having a lot of fun, but really, your system is a lot of work and based on assumptions and requires extra skill (to know that you have actually saturated the solution).
Let me point out that the highest grades I have seen specified by Rio Tinto and others guarantee the sodium tetraborate decahydrate equivalent to be between 99.9 and 105 or even 110 %. That is due to uncertainty in the state of hydration. You do not know how accurately you are measuring when you measure by weight of dry powder or granules if you are looking for an accurate measurement of sodium tetraborate unless you know the exact state of hydration of all of your batch.
Originally Posted by Kirk Keyes
I don't see your argument that I do not know if I have a saturated solution. If I decant a clear liquid and cool it, I will soon know if it was saturated. If it sits long enough with excess borax at the bottom, and I stir ir periodically, I don't see how it cannot be saturated. If I weigh an accurate 4% solution to the nearest 0.1 gram I am certainly more accurate than measuring a solid whose concentration, so to speak, is not known any better than +/- 5%. The best way I can see to make sure of the state of hydration is to make a saturated solution. It must be commonly used as a method, for the weight percentage of borax decahydrate in a saturated solution is specfied vs. temperature to the hundredth of a percent in the Borax Decahydrate Product Profile by U. S. Borax.