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.
"MC"? I'm missing the abbreviation.
I think he means 20 Mule Team Borax. (He'd previously abbreviated this to "Mule crap.") IMHO, a poor choice of abbreviation, particularly for this thread, which began as one on metol/ascorbic acid (aka "MC") developers!
"MC"? I'm missing the abbreviation.
Kirk, you spelled out "mule crap" in your previous post. I just abbreviated that.
Potassium tetraborate is about 25 times more soluble in cold water than the sodium. By the difference in solubilities we could get a first solution that removed 95% of the soluble impurities in sodium tetraborate at a cost of about 5 grams of borax decahydrate. We pitch that, make another solution in cold water from the sediment removing 95% of remaining impurities and leaving about 90 grams. The soluble impurities are down to about 2 ppm. If that is not good enough, the process could be repeated using another 5 grams and leaving a fraction of a ppm.
I doubt you would have any difficulty getting Pharmaceutical grade from Rose Hill. IIRC, its about $2 a pound in 50 pound bags.
If you can filter instead of decanting, you could probably get 98% of impurities out at 1 pass.
I got tired of repeating 20 Mule Team Borax some time ago, and since the original stuff was pulled out of Death Valley behind a bunch of mules, it seemed appropriate. I call my own batches MCB, so maybe it's a low grade of MC.
Originally Posted by srs5694
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You neatly make 2 posts and sidestep my post. Interesting.
I am sorry you choose to ignore the post I made with the refereces you missed, but I am getting tired of arguing this back and forth. I am not against you, but am against passing on bad information.
What more do you want from me.
I did not see this post before I wrote my previous one. I do not have a book by Mees with over 700 pages. There is no mention of the word "potassium" on p. 400 of Mees & James that I have. The only mention I found in regard to fixers was that a bit of potassium iodide in a fixer would speed up the wash time.
I probably would know more about these things if I made my own fixer, but I prefer to buy the best from those who do make it.
I am wondering more how potassium salts would be any more than trace amounts in borax and why they would not be given a minimum allowable number in the ANSI-PSA Standard. At any rate, it is 25 times more soluble than sodium tetraborate, and most potassium compounds are much more soluble than sodium tetraborate, so the method of fractional solution ought to minimize it quickly.
I should have said "maximum allowable".
The references I give are real. My Mees and James is the third edition and the paragraph is under "Thiosulfate Cation", but since you failed chemistry you may not know that Cation means positive ion including Cacium and Potassium.. Mees and James is not as good as Haist, which I helped edit.
I'm sorry, but I'm tired arguing this with someone who failed chemistry and now I see why. Please forgive me, but this is just exhausting to me. Neither I nor Kirk nor others can make you see your errors.
I'm not saying that potassium is present in large quantities in Borax. I'm saying that if it is it is a problem and should be in the ANSI standard or ISO standard for photograde Borax.
Your argument of chemistry with chemists, particulary photo chemists is misleading everyone, including yourself, and it is best you stop now.
I will not argue against your experience with NASA, but you insist on arguing against my experience and others in the field of chemistry which you admittedly failed. You cannot even find the reference in a textbook.
Forgive me, but this is true.
Well, I was doing quite well in chemistry through inorganic, qualitative and quantitative analyses and chemical engineering lab. I have found that the only thing of real value that one learns in school after the basics, which I new before I went to school anyway, is how to learn more. I do know cations and cathodes and anions and anodes and a lot of other things. There is NO mention of potassium on that page under that heading or any other. Lithium, calcium, sodium and ammonia are discussed but not potassium. If you want to come look at my book, I'll get you a bottle of some really good local wine and we can go over it together. My copy was printed in 1969.
I reread the chapter on procesing after development beginning on p.397 and ending on p.407 in my 1969 edition. I found three references to potassium. The first was the one about adding some KI to the fixing bath speeding up washing.
The second was on p.401:
"Strauss found that sodium chloride acts as a fixing accelerator whereas sodium bromide has some retarding effect, although Sheppard & Mees found that 0.1 M potassium bromide had no effect on rate of fixation."
The third was on p 402:
"Where potassium alum is used as a gelatin-hardening agent in an acid hardening fixing bath, the retention of argentothiosulfate ions is greater."
I do not mean to imply that you are wrong, but that I had at my disposal no means of proving one way or the other. It is pretty obvious that my edition is not the same as yours.
I cannot imagine what borax would be used for in an acid hardening fixing bath. Boric acid I could see, but the culprit here was potassium alum, presumably in much greater quantities than any that might come in with impure sodium tetraborate.
It is also pretty obvious that my edition came out before the TMAX series.
My copy of Mees has over 1100 pages and is a standard book size (about 7x9 in) but very thick. Mees and James is a larger book in length and width, about 9x11 and thus has fewer pages.
In the Mees reference above and in Haist, they show plots of activity and potassium salts are 4x slower than sodium salts in fixation. Calcium also appears to slow rates.
Haist gives the actual reference to additional work, and there are published patents on how to overcome the deleterious effects of potassium ion on fix rate.
AFAIK, potassium salts have no significant effect on development, but do have an effect on emulsion precipitation.