The speed-loss of that last graph is only 1/6th of a stop. As both you and Rudi suggest, this is tiny and may be solely due to normal experimental variation. I only did one experiment at that ratio of 117. The problem is, it takes me a couple of hours to run one experiment. My steps are:
Originally Posted by Photo Engineer
- put a film-strip in tank, held down with magnets.
- measure and mix chemicals to make 100 ml of test-brew (slow when adjusting pH to a target at 20C).
- bring developer and water-bath for the tank to 20C.
- develop, stop, fix, wash, dry.
- measure densities w/ densitometer.
- type them into computer and graph them.
- if it looks promising: compare grain/sharpness with loupes, and scan strip into computer.
- ponder what to try next.
As a result, one experiment is one evening. So an array of tests, such as trying various amounts of some chemical, means using an array of evenings, and/or all day Saturday. And that's doing each experiment just once. And that's doing just strips, not whole rolls. Back in the day, did Kodak's engineers have testers or technicians available to do much of this tedious work for them? If so, that must have been great.
I'm thinking it might be worthwhile to run longer strips containing two frames instead of just one. That may give most of the advantages of two identical experiments, yet consuming little extra time. Any thoughts about how to speed up experiments?
@kb3lms: We're getting closer! The formula is now fairly stable, so now I'm thinking of things like chelation and improving convenience.
I fully understand. I was just making a point regarding that tiny difference. I would consider it a non-difference!
Another question for those who know chemistry:
How much citric acid is needed to chelate calcium and magnesium in hard water?
My analysis below says 1 g/L. But is this analysis correct?
Water is consided "very hard" if it contains over 180 ppm of metal ions. Let's assume we have 200 ppm. That's .2 g/L. Let's assume it's all calcium. The atomic weight of calcium is 40 g/mole. So have .2/40 moles/L of calcium in the water. Citric acid has a molecular weight of 192 g/mole. And assume each molecule of citric acid can chelate one atom of calcium. That means we need (.2/40)*192 = 0.96 g/L of citric acid to chelate that calcium.
Magnesium is lighter, weighing 24 g/mole, so we'd need (.2/24)*192 = 1.6 g/L of citric acid to chelate solely magnesium. But I'll assume that hard water contains mostly calcium (is this true?), so closer to 1 g/L of citric acid is sufficient.
Or did I goof?
BTW, I'm ignoring the problem of the Fenton reaction with iron which slowly destroys the ascorbate. That reaction occurs over days or weeks. My immediate goal is to prevent the developer from becoming cloudy after 45 minutes due to calcium and magnesium precipitating out of hard water. Also, to maintain pH, the citric acid will need to be countered by considerably more sodium metaborate, which will improve buffering.
Citric Acid is a poor chelaing agent. This means that 1 mole of CA does not complex with 1 mole of Ca++.
Now, assuming that 1 mole of Ca++ = 1 mole of CA, then your figures are ok, but you need an excess. If you look at the sequestrant levels in most developers, you find that it is about 2 - 5 g/l for strong sequestrants.
You guys were right! I re-ran the experiment this evening, but boosting the AA even more, which should have cut the speed even more if my theory were correct. Instead, I got this curve:
Originally Posted by Photo Engineer
This graph thinks the film-speed is a hair *higher*. I stand corrected: the amount of AA has no effect on speed.
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That's the reason why I wanted to know at which level speed or other properties deviate by more substantial amounts. I assume you have the data right in front of you from the many experiments you have done by now. If you look at Pat Gainer's results (here and here), you shouldn't expect much difference even with big changes in AA amount.
Originally Posted by albada
Trying to be the best of whatever I am, even if what I am is no good.
Today I did what Microsoft calls, "Eating your own dog-food." I developed an important roll in my own developer. Here's the latest concentrate:
Propylene glycol ......................... 23 ml
Sodium metaborate (4 mol) ....... 4.7 g
Ascorbic acid ............................. 6.5 g
Phenidone ................................. 0.05 g
Propylene glycol to make .......... 30 ml
Compared to earlier formulas, I boosted metaborate and ascorbic acid to improve buffering in order to make the developer more tolerant of errors in measurement of sodium sulfite. To make 1 liter of working solution, first mix 30 ml (45 grams) of sodium sulfite into the water. Then add 30 ml of concentrate. As a convenience, the dev requires the same volume of sulfite and concentrate (30 ml/L each), so you need to draw only one fill-line on your little beaker. pH is 8.15 to 8.17. Time at 20C is about 1.9 times XTOL's time.
I was frugal and mixed only 200 ml of solution, the bare minimum for a SS tank, and developed one roll of TMY-2 (Tmax-400). The results are best described as "strong": Leader-density is 3.0 to 3.15, and edge-markings are a little denser than XTOL's. In my past experience, developing a full roll (36-shots) resulted in lower density than in test-strips. This dev broke that rule: The roll is just as dense, or a little denser. Perhaps this is due to the strong buffering.
By the way, I pre-washed the roll, and I always pre-wash test-strips. I discovered in March that TMY-2 gives me higher density when I pre-wash it. You can find discussion of this in older threads.
The event was a wedding, and I noticed two men in the parking lot fixing a van:
And here's a full-resolution crop of the neg-scan:
The grain is plenty fine. As I saw in test-strips, this dev looks like XTOL. So I'm getting close. The formula above needs a tweak or two, and much more testing. Comments are welcome as always. A question that I'm not entirely confident about is whether it's worth boosting the buffering as I did. Or is that just a waste of chemistry?
Mark, thank you for working on this developer. I have been following your discoveries with great interest, as XTol 1+1 is the only film developer I use. I was wondering if you had any data, by now, about the keeping properties of the concentrate, since quite some time has passed since you begun.
Many thanks, and good luck.
See post no. 10 here:
Stock solutions mixed in glycol should last at leat 2-3 years.
But Xtol concentrate contains some water of crystallisation from the metaborate.
I am running a 1 year test on early Xtol concentrate D-316 due to complete Jan 2013 which should show if this water of crystallisation has an adverse effect on shelf life.Even if it does it should be possible to make a recommendation to heat the concentrate when it is made, to drive off this water.