It's not polyethylene glycol that is used to mix Pyrocat HD part A, but propylene glycol. The only reason for using it is to make a very long lasting solution.
Wanting to try reversal processing but also not die
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See post #10 in this thread: https://www.photrio.com/forum/threads/mixing-pyrocat-hd-from-scratch.5517/
That's very strange and it's the only time I've seen using polyethylene glycol to make Pyrocat HD part A. Propylene glycol is what is suggested.
@Raghu Kuvempunagar Besides, polyethylene glycol is a relatively vague term and includes many different compounds with widely different molecular weights. PEG 4000 for instance is a solid, you can't dissolve anything in it.
This was a wise advice, I fully agree with that strategy, the more we can avoid solvency the better the process is.
Pyrocat in glycol Solution A concentrate is made in Propylene Glycol (https://en.wikipedia.org/wiki/Propylene_glycol), I guess only for a better keeping and shelf life. IIRC the glycol version uses the same times than the original water version, so I guess it has no impact in developer strength.
Pyrocat in glycol does not contain PEG polymer ( https://en.wikipedia.org/wiki/Polyethylene_glycol)
PD: sorry, that was clarified yet by Anon
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See post #3 in this thread: https://www.photrio.com/forum/threads/glycol-tea-and-glycerine.3680/. Also see my post #203 above. Tom knew his stuff - he used PEG for part A of Pyrocat-HD.
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Raghu, no known formula of Pyrocat uses Polyethylene Glycol, in that post #3 a member speaks about PEG, but you won't find a single Pyrocat formulation with it: HD, HDC, M, MC, P, PC... no one uses PEG, versions with a "C" use Propylene Glycol. Some versions use TEA or ascorbic that have an impact in developer activity.
https://www.pyrocathd.5x4.co.uk/mixing-pyrocat-hd/
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See post #203 above where I quoted Tom Hoskinson on using PEG for part A of Pyrocat HD. Also see post #3 in https://www.photrio.com/forum/threads/why-pyrocat.102378/:
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And then check post #4 & #24 in the thread you link to.
It's an easy mistake to make when typing too fast.
Raghu, this an interesting post about Pyrocat in PEG : https://www.photrio.com/forum/threads/mixing-pyrocat-hd-from-scratch.5517/#post-73343
Tom explains to Sandy he is using PEG. This was 16 years ago...
PEG is not that difficult to obtain, but Propylene Glycol is a very common food grade ingredient with dozens of offers at Amazon (https://www.amazon.com/propylene-glycol-food-grade/s?k=propylene+glycol+food+grade)
Almost nobody uses PEG for Pyrocat , no "official" formulation includes it and no wet kit can be purchased including it. But it is true that several individuals made that substitution, this is not new in the DIY mixing of developers, always some have substitued some ingredients by other equivalent ones.
I guess that we may agree that some few individuals substitute Glycol by PEG in home mixed concentrate, with no difference in the development times.
In the case of the Jim Noel, a true wise master, it was an spelling error, https://www.photrio.com/forum/threads/why-pyrocat.102378/#post-1355218)
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It's interesting to note that Formulary sells PEG and the product description says this:
"Polyethylene glycol is non-toxic and is used in a variety of products including as a component in some developer formulas".
What are these developer formulas? And what's the role played by PEG in them?
"Polyethylene glycol is non-toxic and is used in a variety of products including as a component in some developer formulas".
What are these developer formulas? And what's the role played by PEG in them?
Well, for example in reversal developers, as I've learned in this thread.
Lachlan suggested:
"enabling much better penetration of the developer components into the totality of the emulsion(s), which then develop at a more simultaneous rate (likely from knowledge from colour processing research- which seems to have been the background of at least one of the Agfa patent holders)"
For color negative processing we have 3 emulsion layers, and the deep one has to keep the development pace...
It would be interesting a side by side, but IMO the glycol or PEG in Pyrocat are only "excipients" that are better than water to make the concentrate, as the mix is more unstable in water. I'don't know if a clear benefit may be obtained from PEG, the fact that in 16 years that substitution has not been popular at all suggests there is no clear advantage, but...
Another Pyro modification was ascorbic addition, which is important to prevent developer oxydation in rotary processing which increases "general stain" (stain as fog), this has an impact in the developer behaviour because ascorbic is an agent, instead glycol variants were only intended (IIRC) for a better preservation of the concentrate.
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It accelerates the rate of development via several means including letting the gelatin swell better allowing fuller, more even development. They may also be added to the emulsions along with PVA's, PVP's etc for the same purposes - likely more commonly in colour emulsions to even out development rates. I think Fuji Neopan 1600 was essentially a Neopan 400 variant with a development accelerator added to get the 1600 development time about the same as Neopan 400 at 400. From Ron's book, in unwashed paper emulsions, Photo Flo 200 acts "as a mild development accelerator giving up to a 1 stop speed increase and one grade in contrast depending on emulsion formula".
It's likely dependent on the molecular weight of PEG used - a low weight one may have little effect - but I always take the view these sort of developers attract followers whose actual process control abilities lag far behind what they think they are. You have to remember that there's a lot more opinion than science in most commentary on Pyrocat.
Well, if using PEG as excipient then it should be of low mollecular weight to be liquid... so little effect...
Staining developers may deliver a fine grain, as the silver developent is lower for the same density... but also Xtol delivers a fine grain with lots of acutance.
My view is that very linear films like TMX may deliver dificult to (optically) print highlights, as density may easily skyrocket. Certainly Pyro stain blocks more the blue in the highlights than in the low densities because stain color, so with VC paper highlights are printed with an effective lower contrast grade, helping its depiction. IMO the stain solves that shoulder lack "pitfall".
Nothing wrong in using a linear film or in using Pyro, both are great choices, but if praising the linear curve and later saying Pyro is a marvel then this is not understanding that the actual pitfall was not having a shoulder in the curve.
There is the 2nd advantage, making a negative that can be printed both on silver photopaper and on alternative, as pyro contrast is boosted for UV light.
My guess is that the stain effect in the highlights with VC paper was not well explained for many years, many that were still using graded paper saw no effect, while those using VC saw it, so all was about opinions. But, LOL, the thing was about praising the lack of shoulder, and later not knowing how that pitfall was self corrected with the Stain vs VC paper interaction
_________
The other interesting mess was the 1960 ASA speed change, 60 years later there is ZS confusion about if metering for Z-V or for Z-VI, or if rating with the box speed or the half.
The pyro effect generated a similar degree of confusion !
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The AGFA-Gaevert patent mentions that the use of PEG also resulted in fog which reduced DMax. They had to use 5-methylbenzotriazole as antifoggant to deal with the fog and apparently other antifoggants didn't work well. In summary, use of PEG as development accelerator is not straightforward. It's a complex game involving a specific developing agent and a specific antifoggant.
Xtol is designed to use solvency to get at the iodide in modern films, enhancing sharpness, staining developers aim to use dye density to allow development to a lower silver density allowing for potentially higher sharpness - much the same effect can be achieved with more conventional developers if you aim the negative to print on to higher grade of paper.
Shouldering is more of a problem - a a linear highlight can be brought in range by various means & still look very good, but if you've hit the top of the shoulder of film that tends to shouldering, separation won't look as good when burnt in. The dye image density effect of pyro (and consequent lower silver CI's being used) may mean that films that shoulder will do so later, and/ or (if the stain is yellowish) effectively bring highlight contrast down. That said, it also matters that you give the film sufficient exposure and sufficient processing to get the shadow values to look 'right' without having to go to such a high grade that highlights become trickier to bring in.
Only in the HQMS variants. Use the MQ one, unless you really cannot work with HQ.
Of course using the shoulder and toe of the film requires an accurate metering and mastering the particular film/processing. For complex scenes, the more we nail the tonal manipulation in the negative the less manipulation work we have in the printing, but any pitfall will have an impact. Instead with a linear film we have a more flexible negative, YMMV, I guess.
But regarding reversal processing, we don't have much that post opportunity. We can always bracket, but shooting slides is more challenging because we should nail the job... to me for metering slides we need similar skills than when metering for negative film when wanting to use the toe/shoulder, we need accuracy and preferably using spot metering.
But regarding reversal processing, we don't have much that post opportunity. We can always bracket, but shooting slides is more challenging because we should nail the job... to me for metering slides we need similar skills than when metering for negative film when wanting to use the toe/shoulder, we need accuracy and preferably using spot metering.
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Neither are difficult if you have a meter that reads out in EV & (ideally) has the ability to highlight or shadow index using the IRE scale. IRE 1 for the darkest shadows with detail on neg stock, IRE 10 for the brightest highlights you want to retain detail on transparency. An incident meter is no better or worse than a spotmeter. Extreme contraction or expansion are often much less necessary than the macho tales on the web & in books & magazines would have you believe. Most people pretty quickly find lighting situations that work for their sensibilities and the rest of their process adapts pretty fast.
On the subject of permanganate bleach, I made an observation last night. I mixed the following bleach formula in deionised water:
20g sodium hexametaphosphate
1g potassium permanganate
50g sodium bisulfate
Top up to 1000ml
My previous formula was the same, except the omission of sodium hexametaphosphate and seems to bleach fully developed film leaders in a minute or so. My previous bleach would come out of the tank with a slightly different colour. Instead of the dark purple of permanganate, it would take a more reddish, perhaps slightly brown colour. This time, the bleach with 20g/l sodium hexametaphosphate came out exactly as it was, which I believe is a good sign.
20g sodium hexametaphosphate
1g potassium permanganate
50g sodium bisulfate
Top up to 1000ml
My previous formula was the same, except the omission of sodium hexametaphosphate and seems to bleach fully developed film leaders in a minute or so. My previous bleach would come out of the tank with a slightly different colour. Instead of the dark purple of permanganate, it would take a more reddish, perhaps slightly brown colour. This time, the bleach with 20g/l sodium hexametaphosphate came out exactly as it was, which I believe is a good sign.
Would be good to know how long this version of permanganate bleach will keep well - hours, days, or weeks.
Yes, I've kept this bleach and I'll let you know how well it keeps.
That's because HexMePh inhibits the formation of MnO2 deposits, the brown-red color you saw with your previous version of the bleach.
This new bleach is said to keep form months.
This was Mr. Ruddy 's view too.
You added sodium sulfate and this was not the original formula. This is in order to try to tame this solution and control its aggressiveness,
- But you permanently deleted sulfur sorrel. Why?
You could add sulfuric acid as the original formula states, and at the same time add 100 grams sodium sulfate, two grams permanganate and the rest of the formula as the original formula states.
Deleting sulfuric acid will benefit one side and may harm another side.
- You should hold the stick in the middle, my dear colleague.
deionised water 700 ml
Sodium potassium hexametaphosphate....... 20 g
Potassium permanganate ............................. 2 g
Sulfuric acid (20% by weight) ...................... 27 ml
sodium sulfate ............................................ 100g
make up to 1000 ml with water (p.H = 1.4)
They will do that.
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I added sodium bisulfate, not sulfate. This is a substitute for sulfuric acid and works fine. Instead of using H2SO4, I used NaHSO4. This might also reduce emulsion softening from permanganate a bit, but I can't be sure about it, I haven't made any side by side tests.
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