Firstly: Alan: Thanks for doing the D-316 testing, and for the link about storage. I hadn't seen those postings.
Originally Posted by Rafal Lukawiecki
Rafal, I have no results from long term tests yet. But I have some short term failures. For example, in one experiment, a concentration-ratio of 0.46 resulted in crystallization after a couple of weeks. I'm now testing a ratio of 0.40. The purpose of these ratio-experiments is to see how high concentration can be.
The concentrate (and sodium sulfite) will last longer if stored in the refrigerator or freezer. A few months ago, I put some concentrate in the freezer, and got no precipitation. If frozen, I would expect it to last for many years. Of course, you must remember to take the two bottles out of the freezer a few hours before you need them.
Here's one of my favourite shots from the wedding, following my policy of "be there at the wrong time." I caught the tear-down:
Do you see any grain? Me neither. This is why I'm eager to create a clone of XTOL, and I hope this photo shows that the concentrate succeeded.
Here's a question that perhaps only PE can answer (but anyone is welcome to try):
The curves below show two XTOL strips averaged together (red), and two strips from the formula used for the wedding (green and blue):
Note the right quarter of the graphs. The red XTOL graph rises only slighly in the right quarter, but the two wedding graphs have a more pronounced rise there. My earlier developers with less buffering (and AA) don't do this. But I do see it in one earlier dev with more buffering (and AA), as well as the latest two strips. So I think that right-rise is real. I'm guessing it's caused by either (1) boosted buffering, or (2) boosted ascorbic acid (AA) which is a secondary developer. This developer is rather dilute, so I'm surprised to see a boost in highlights instead of compensation that one normally expects with dilution.
Any idea why boosting buffering or AA would cause highlights to have higher slope than shadows and midtones?
Can the curve be linearized?
I was thinking of adding KBr, but that's not soluble in PG. Maybe benzoic acid? Other ideas?
I know the right-rise is small, but I'm a perfectionist who'll go for linear if possible.
If you are at the limit of the buffer's capacity (which can take place at the densest part of the negative) then you can get a downdurn. This may be a case of film and developer being built together to give the proper curve and image quality and therefore your developer here is overdoing some aspect that should be more restrained.
If that is the case, then I would expect some degradation in the image structure in your developer wrt the XTOL.
That is what I am guessing at this stage. Your developer is overdoing things and should have less buffer. In its present state, your developer will suffer in grain or sharpness or both wrt XTOL.
Thanks for the response. That dev has both high buffering and a large AA/Phenidone ratio, so I'm thinking of running experiments (evenings...) to separate those two factors. "Overdoing things". The purpose of that was to tolerate errors in volumemetric sulfite-measurement, and that made me think of...
Originally Posted by Photo Engineer
----- Here's an idea for measurement -----
I thought of a way to accurately measure sodium sulfite by volume, using a typical little beaker or medicine cup:
Step 1: Pour the correct amount of liquid concentrate into the cup (up to a fill-line).
Step 2: Add sulfite until the liquid reaches a second higher fill-line.
Step 3: Pour the cup into the main beaker containing water and mix.
This works because the liquid drives out the air between the sulfite particles, so you're only measuring the volume of solid. I tried this using only propylene glycol (PG) in a graduated beaker. I first poured in some PG, then added a known weight of sulfite, and measured the level. This let me measure the specific gravity of sulfite, and it was accurate within 1%! Success! Except...
The problem with this method is the sodium sulfite becomes a sticky glob in the bottom of the cup, perhaps due to trace water in the PG. It won't pour out, and must be helped with a popsicle-stick or somesuch. To get it all out, the little cup should then be rinsed in the beaker (dipped a few times). Would folks be willing to do this?
----- Here's a 2-bath idea -----
Since these developers consist of concentrate and separate sulfite, I realized they could also do double-duty as two-bath developers. A normal A-then-B development would be too thin, so you'd cycle back and forth between A-bath and B-bath a few times, spending 2-3 minutes in each bath. You should get compensating development typical of two-baths.
Cycling back and forth will contaminate each bath a little, but that won't matter because these developers are one-shot. Also, you'll need to mix say 50% more dev in each bath, and develop using the A-B cycling for a longer total time.
It would be appealing to have one developer that can be used either as a conventional single-bath or as a two-bath.
I've got more ideas than time to experiment with them. Retirement is sounding good!
Comments on all this are encouraged.
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The wedding formula has much ascorbic acid, and much metaborate for buffering. I decided to eliminate these variables separately. Following PE's rule of "never do one test", I ran two strips with a formula having less ascorbic acid. Here are their graphs:
Here's the formula. Note the addition of citric acid to maintain pH:
Sodium sulfite .................. 45 g
Sodium metaborate .......... 5.4 g (very high to give strong buffering)
Ascorbic acid .................. 4.5 g (a normal amount; AA/Phen ratio=90)
Citric acid ....................... 1 g (brings pH back down to 8.16)
Phenidone ...................... 0.05 g (developer)
Propylene glycol ............. 23.5 ml (amount needed in a concentrate for 30 ml/L)
The good news is the right-side rise seems to be gone. But I notice that both graphs have a bit lower EI and a bit higher contrast compared to XTOL and compared to what I was getting with earlier formulas. These differences are probably too small for folks to notice, but I'd like to know why this is happening. I'm mixing propylene glycol into the water to simulate a concentrate, and I'm wondering if PG reduces EI slightly, or if that's due to the very strong buffering, or if the citric acid could do this. So I'll try reducing metaborate and eliminating the citric acid, unless you have a better idea.
Again, the graphs show less difference than slight variations in temperature, agitation or other processing parameters will give you. If you want to lower pH without adding a new ion (citrate) to the mix, you could replace some of the sulfite with metabisulfite. Not sure it makes a big difference, but it should reduce complexity. If you reduce amount of metaborate, you also reduce buffer strength, i.e. you turn more knobs at once.
Originally Posted by albada
Trying to be the best of whatever I am, even if what I am is no good.
You are correct. But don't forget that I am a perfectionist trying to tame that variability. That approach works well for software I write, but I'm finding that this is a different animal. I have another motive for adding citric acid: chelation. Though PE says there are better chelators out there, citric acid is easy to obtain and will hopefully extend the 45-minute limit after mixing in hard water.
Originally Posted by Rudeofus
Today, I tried something different: I replaced the metaborate with TEA. The results look great. The density-curve is a nearly perfect match to XTOL:
And the grain and sharpness look the same as well, and JPEG sizes are within 1%:
TEA soup: XTOL:
Here's the formula for the concentrate:
TEA (99%) ...................... 20 ml (22.5 g)
Propylene glycol .............. 5 ml
Ascorbic acid ................... 4.5 g
Citric acid ........................ 4.2 g
Phenidone ...................... 0.05 g
Propylene glycol to make 30 ml
Target pH = 8.16-8.18.
For TMY-2: 11:30 minutes at 20C.
A litre of developer contains 30 ml of concentrate and 45 g of sodium sulfite.
TEA has a number of advantages:
- Stronger buffering due to large quantity (helps with variable sulfite-measurement).
- Concentrate will hopefully not crystallize.
- Phenidone can be replaced with Dimezone S (try 0.1g in the above formula).
- With TEA, pH drops as temperature rises, giving some auto-correction of temperature.
- Avoids borates which damage citrus trees.
And TEA has some disadvantages:
- It's harder to locate in some areas.
- 85% TEA is also available, potentially causing inconsistency.
- It's too viscous and must be thinned by another solvent (I used propylene glycol above).
Anyway, I mixed the formula directly into water, so I don't know if all that ascorbic acid and citric acid can dissolve in 25 ml of solvent. There's only one way to find out: Mix it! I also want to try that 2-bath idea I mentioned a couple days ago. If that works, this concentrate will be very useful, giving XTOL quality when used normally, and a push with low contrast if used as a 2-bath.
What do you think about all this? And should I go with the metaborate formula in propylene glycol, or this TEA-based formula?
Finally, a question for chemists: Is 4.2 g/L of citric acid enough to chelate all the calcium and magnesium in hard water? If so, that would be another advantage of the TEA-based formula.
Last edited by albada; 10-21-2012 at 02:41 AM. Click to view previous post history.
It is hard to answer your question about chelation as Citric Acid is a poor chelating agent and water contents and quality vary all over the world. Run a keeping test vs Xtol is what I suggest.
A keeping test will only tell us whether the concentrate keeps, but won't tell us much about the effectiveness of the citric acid chelating agent against hard water. I'm quite confident that citrate won't tie up iron enough to render it ineffective against the Ascorbate.
Here's my take:
- You can find chelate stability of various citrate salts here.
- The strongest competitors for Ca2+ in any film dev will be sulfite and carbonate. Carbonate also competes for Mg2+.
- With estimates for ion concentration and the numbers taken from the linked pages above you can calculate whether Ca2+ or Mg2+ will likely precipitate.
Trying to be the best of whatever I am, even if what I am is no good.