Decided to do more testing with the EXF “Pharoh Lith” series. I found my way into a very interesting developer, though not ideal for all lith printing subjects. It definitely uses hydroquinone as the primary developer, and the blacks get nice and deep while highlights stay fairly gentle. However, midtones still develop relatively fast compared to black development. The end result is that this developer works great when you want to make a higher contrast print (say grade 4) with enhanced highlights, but it gives poor results when trying to make it lower contrast with more exposure, because everything becomes midtones that develop quite fast and it’ll be hard to get a good black level without all the midtones being fairly dark.
The formula I used:
2g of hydroquinone in propelyne glycol (20ml of 10%)
4g of ferrous sulfate heptahydrate
60ml of triethanolamine (TEA)
0.6g of bromide
0.5g sodium hydroxide
12g potassium carbonate
Final pH ~11
2L of developer topped with water
The ideal order of mixing these components isn’t determined yet. The ferrous sulfate, hydroquinone, and TEA all react with each other and their environment in different ways. The exact order I mixed was ferrous sulfate, TEA, and carbonate in 2L. Then pour in the hydroquinone, then add the hydroxide and bromide. I’m fairly certain this is not the ideal method of mixing to avoid iron sludging that’ll stain prints though. The carbonate and hydroxide each do different things and I’m fairly certain that the ratios of them need optimizing.
This developer is a departure from EXF1, as it does not appear to give an iron image and will instead give fairly warm olive tones and colder shadows on warmtone paper. Fairly typical of a lith developer. Unlike a typical lith developer though, this will show consistent activity levels for at least 2 hours or 16 8x10 prints, and features a fairly fast development time at room temp. It is optimized for non-lithable Ilford RC papers right now. I tried some lithable paper and it developed too quickly and with no tonal separation. I believe the surplus of HQ is to blame there.
The exact chemistry of this developer is complex and probably beyond my capability of understanding, much less explaining, but I’ll try anyway. So, there is 4 different interactions in this developer. The end result is that the HQ is kept alive at a constant level for a relatively long time.
HQ: Oxidizes from exposure to oxygen in an alkaline environment to Q (benzoquinone). Also can oxidize to a semiquinone when developing (semiquinone is the key ingredient of infectious development). HQ will also oxidize Fe or Fe3 and convert to Q, while the semiquinone will oxidize Fe and Fe3 and convert to Q. The semiquinone will oxidize (I think) with oxygen to form either benzoquinone, or a degraded polymer quinone which can’t be reversed.
Ferrous (Fe2) Sulfate: Is photographically active in an acidic environment but seemed to have very little developing effect when at pH 11. Will reduce Q to HQ and convert to Fe3 ferric ions/sulfate (?). Also easily oxidized by oxygen in an alkaline solution to convert to Fe3. Can also combine with carbonate or hydroxide to form Ferrous Carbonate/Hydroxide. Ferrous carbonate seems to not be capable or extremely weakly capable of developing silver, but hydroxide appears to be capable and is why EXF1 has an iron image. Both compounds are only barely soluble and will mostly precipitate from solution.
TEA: Is a known silver solvent at the concentration being used but also functions as a chelating agent, capturing stray Fe2 and Fe3 ions. Seems to be inactive to HQ, but interacts with all iron atoms. It will reduce Fe3 to Fe2, and then Fe2 to Fe in an alkaline (>9 pH) solution. The exact reaction speed and conversion rates between each form of Fe varies depending on alkali used, even if kept at the same pH. Probably due to reaction differences with carbonate vs hydroxide forms of iron.
As you can see, definitely a lot going on, and why balancing this developer for ideal results will be more analytical than most things I do. Too much TEA and you end up with metallic iron that’ll oxidize the hydroquinone. Too little and the Fe2 won’t be stable. I believe the lack of midtone separation here is due to these ratios being unbalanced. In the middle there was some iron specks, but near the end there was absolutely no metallic iron I could see in the developer. In the middle the solution was more orange rust colored and clearly colored but transparent for the first hour (ie, I could see the print fairly well). As more printing and time passed it grew darker in color and with a more reddish hue, typical of oxidized hydroquinone developers. Throughout all development it had some very fine powder present which didn’t immediately sink to the bottom (ie, probably not metallic iron).
So, given the progress and end result, here is my hypothesis for how it is unbalanced.
Too much hydroquinone being kept alive, hence the overeager midtones. With less I believe that infectious development would be more of a source of development rather than hydroquinone itself. In a previous test with half the HQ, development speed was significantly reduced though
Unknown for sulfate? The solution should’ve stayed at least semi green for a while longer than it did. TEA is documented to preferentially reduce Fe3 to Fe2 before Fe2 to Fe. In theory with proper balancing, there should never be any Fe in solution. If I add less then in theory there is less Fe2 to be reduced to Fe. The Fe2 amount should be enough to keep the HQ alive and nothing more.
Unknown for TEA? I can’t tell if I should add more or less. With less there wouldn’t be any reduction of Fe2 to Fe, but also I believe overall tray life is definitely dependent on TEA amount, with the sulfate being more of a balancing agent that determines the rate of HQ decay. With more however there would probably be more reduction of Fe2 to Fe. Making sense of the cycle of interactions and metastability makes my head hurt.
I think for now I’m going to keep things simple with changes and try reducing hydroquinone and sulfate by half or even to a quarter, and keeping everything else the same aside from needed pH adjustments. In theory with less sulfate it would always just be kept alive by the TEA and more slowly restoring the HQ, giving more time for infectious development to occur from semiquinone activity. If there is any excess then it simply decreases HQ in solution and increases iron sludging problems. My hope is that TEA in such a balance doesn’t do much other than act as a weak silver solvent (ie, reducing grain) and otherwise sacrifices itself to keep both sulfate and HQ alive until eventually it’s completely oxidized and the developer is completely dead.