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.
You are doing your measurements qualitatively using the Mark I Eyeball which in your case is now over 80 years old IIRC.
I did mine with the IB sensitometer and the Macbeth densitometer and did it qantitatively.
I trust mine, and I trust the differences that I have seen. Papers can sense as little as 100 milligrams difference in bromide or chloride concentration in a liter of developer. It affects speed and curve shape both. In some papers, it affects fog as well.
Yes, but I was talking about film. I do use metaborate in paper developer, but that's a different animal from the one we've been discussing. I do have a densitometer that I designed and built that can read to .005. Besides, if the tech borax meets specs, a saturated liter would have at most about 0.028 grams of sodium chloride.
The highest grade I have seen from Rio Tinto specs is NF, a pharmaceutical grade, which lists only heavy metals at <20 ppm. The difference between Rio Tinto Tech granular and powder is ONLY in the water insoluble particles, which are <400 ppm in the granular and none in the powder. The variance in measurement of percent borax decahydrate is in the water content, which will vary with storage conditions due to changes in humidity. the same variance can occur in any grade, including AR.
Originally Posted by Kirk Keyes
Your AR grade assay was for a particular sample of known hydration
If a cheapskate is using alternate-sourced borax instead of 'photo grade' (or photo company supplied), for cost reasons, then there will be a limit to how much lab refining the cheapskate is able/willing to spend time/money on. A 4 liter Pyrex beaker probably costs more than some of my other stuff and more than my chemicals combined.
I may be in the cheapskate category, but I'm sure I spent more buying bulk chemicals than I could have buying packages of developer, because I would have more fun with the DIY approach.
I DO find the discussion of the science interesting, however.
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Pat - Did does Rio Tinto Technical Grade Powder really say "none" for the insoluble particles? That surprises me as there should be a limit of some sort - i.e a value given in parts per million. As an analytical chemist, I can say that there is always going to be a little of something in most everything... unless you are talking about homeopathic medicine. Did it really say None detected or something, and that is based on the method of analysis, but really doesn't mean that there is "none". Just that that test can't detect any.
Originally Posted by gainer
The AR grade assay had absolutely nothing to do with a "known hydration". Infact, I doubt the hydration was even tested for. It was an "assay", a measurement of the material of interest.
Murray, I'm with you. But it is fun and interesting to discuss the various ways that we can devise to make our technical grade chemicals end up costing more than just buying the recommended grade in the first place.
Originally Posted by Murray@uptowngallery
It's interesting that NF grade only is concerned with heavy metals (as quoted my Pat), and not any of the other substances that the other grades are spec'ed for, like chloride or insoluble matter. It really does point out the differences in the grading system for chemicals and how one should consider these things when chosing a particular grade for a particular use.
Originally Posted by gainer
I don't know that heavy metal, expressed as lead, is the only impurity they are concerned with. It is the only one they listed. There is also a grade SQ for special quality that is granular and has very low allowable maximums of chloride, sulphate and iron. I imagine that the analysis for insoluble material is like the one you described a while back. If you can't see it in the solution and all the solution passes through the filter, whatever is insoluble must be negligible. I figure that if the Powdered Technical grade showed observable insoluble stuff, there would be a comment like < whatever the filter is specified to retain. The powdered and granular have the same specs in the soluble impurities.
Originally Posted by Kirk Keyes
I still don't know the ANSI Specifications for Photo Grade, but have applied for a copy. I don't expect to hear from them until after the holiday season.
I want to make sure everyone knows I am not expecting to produce chemically pure borax by my purification. It is a fractionation method, and since each fraction is less than 1, the final product cannot reach absolute purity until the amount left is 0.
I do not see, given the nature of borax, how a large amount could be stored in a bin so that any random sample would have the same hydration as any other. The manufacturer says that when humidity is lowered some of the borax that started as 10 mol will become 5 mol or even anhydrous. If the humidity becomes higher, the hydration moves back to 10 mol causing some clumping. It is not like NaOH which will form a puddle if left open to high humidity, so I suppose that if your borax were stored at high enough humidity it would all settle out at 10 mol and the percentage of borax decahydrate would simply be 100 - impurities. But if there is not enough humidity in the atmosphere to maintain the decahydrate, what you weigh to be 100 grams of borax decahydrate could be equal in sodium tetraborate content to more than 100 grams. If you purchase it as AR grade, and accuracy of measurement accuracy is critical to your purpose, then it would be well to make sure the the humidity in your storage container stays at the proper value. I don't know what that value is because most uses in developer are not very critical as to weight of borax, however critical they might be in ppm of impurities.
I got the ANSI specs for Photography chemicals sodium tetraborate, pentahydrate and decahydrate, 3 pages ata cost of about $21. In a nutshell, the summary of requirements is:
Assay, Pentahydrate or Decahydrate......101% min, 105% max.
Heavy metals (as Pb)......0.002% or 20 ppm.
Iron (Fe)......0.003% or 30 ppm.
Carbonate......To pass test.
Reaction to Ammoniacal Silver Nitrate.......to pass test.
Appearance of solution........to pass test.
The tests are described in great detail. Kirk or PE could perform them. Most of us have not the equipment nor the skills to perform them.
It appears that the specs would be met or exceeded by the NF grade described at www.borax.com, and the SQ grade would come very close.
You will notice that the minimum assay is greater than 100% and less than 105%.
I have read the spec and it is rather trivial both in content and in testing methodology.
The problem is that my time is more valuable to me than the cost in time and chemistry to run the tests. That is one reason why I prefer to buy the best to start with.