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: 11-17-b8.jpg XTOL: 11-29-b8-XTOL.jpg
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.