To stain, or not to stain – Acid and pyro developers

There is a very controversial topic on the Internet. It’s in fact so controversial that I almost don’t dare post about it. It’s that thing about pyro developers and the dye image (‘stain’) they produce. This is seen as a desirable trait, as it apparently helps to mask film grain, and it adds substantial UV density, which is great for processes like carbon printing. Now, the question is – is it OK to use an acid stop and fixer with a staining pyro developer, or will this obliterate this precious dye image? Come in and find out!

Disclaimer: I’ve always been very skeptical of the story that acid stop or fix would degrade a pyro dye image. Anyone who has ever handled (or even, abused) pyro negatives is aware that the dye stain is pretty darn persistent. At least that’s my experience so far. Furthermore, I’ve been known to use different kinds of fixers, including C41 (which is near-pH neutral) and regular acetic acid fixer, and I’ve also been experimental enough to try a plain water stop bath. Never did I notice any difference in how pyro-developed negatives came out. But hey, you never know.

Let’s get one myth out of the way first. It has to do with the pyrogallol-based developer PMK, if memory serves, and the story went that you were supposed to save the PMK you just developed your film in, and then after fixing the film, dunk it in the used PMK once again. (At least back in 2017 Bob Carnie was apparently still doing this.) This was supposed to add to the stain. Later, this advice was retracted for the simple reason that, yes, dunking the film in the used developer did in fact add stain – but not image-wise stain. In other words, it just added overall density. Basically just dichroic fog.

That’s not what we’re talking about here – I’m only interested in the actual image-dependent stain that adds UV density and masks grain, and that is supposed to suffer from an acid treatment. Well, it’s easy enough to try, so let’s set up a little experiment. Here’s what I did.

I exposed two sheets of Shanghai GP3 film at a random (and somewhat boring) scene. I happened to have a 4×5″ cassette loaded with this film, so it was a convenient guinea pig. It might have been any other film I had lying about, so apart from convenience and chance, there was no particular thought behind this film selection. Both exposures were evidently identical and made right after another on film from the same batch.

I then processed these sheets in Pyrocat HD. The Massive Dev Chart gives a starting point of 10 minutes at 1+1+100 dilution. Now, I happen to be impatient, so I just went for 3+3+100 and 5 minutes instead. Yeah, let’s mix that soup extra strong so we have some density to work with! Agitation was 30 seconds continuous, and then for about 8 seconds every 30 seconds. So pretty close to continuous, if you think about it. Doesn’t matter – what’s important is that both sheets received identical treatment up to this point. Oh yeah, I used that PVC developing tube I made this summer. Not that it matters; tray development would have accomplished the same thing.

Alright, so here the sheets went different paths. The first one went through an acetic acid stop bath (pH 2.0 or so, perhaps even a tad less) for about 20 seconds. I then took some Fuji C41 fixer, mixed it to around 1+5 strength and added a good splash of cleaning vinegar to bring down the pH to less than 3.0. That’s considerably more acidic than the typical pH4.0 or thereabouts that regular acid fixer gives you, if I’m not mistaken. Fixing was also done for about 5 minutes – so far more than strictly necessary, but let’s keep that film in acidic conditions nice and long.

The other sheet had an easy life after being developed. It did not have to go through a stop bath at all (no, not even a plain water stop!) and it went right into C41 fixer. Oh, I did modify that fixer by adding some carbonate and hydroxide so that the pH rose up to 8.0 or so. Just to ensure it wasn’t acidic, you see. This sheet was also fixed for about 5 minutes just by means of ceteris paribus and then washed. Just like the first sheet.

Both negatives during final wash. Acid-processed negative on the right.

I also bathed both sheets during the wash procedure briefly in a weak sodium metabisulfite solution to clear the remaining sensitizing dyes and get as clean dmin as possible. The negatives were washed some more and then hung up to dry by a corner. I used no wetting agent and all washing was done in plain tap water.

Hanging to dry. Acid-processed negative on the right. Oh, the suspense…!

Now, cue the drum roll, as we are ready to have a look at the results! I thought about the ‘purest’ comparison I could make and the weapon of choice is my trusty old (but still quite functional) Epson 4990 flatbed scanner. The advantage of this is that I can scan both film sheets in one go, so that they are absolutely guaranteed to go through the exact same digital workflow. With contact printing, there’s always the possibility of minor variations in materials or processes, and I wanted to exclude these possible problems.

So here’s the first glimpse of an outcome – and actually one that already tells most of the story. It’s a positive scan, which is the type of scan that involves the least kind of under-the-hood digital processing in the scanner driver. In the Epson scan dialog I only set the black and white points in order to use the bit resolution the most effectively. I chose to set the white point in such a way that the clear film rebate still has density. On the dmax I was a little less fussy; as long as we can visually compare the highlights in the inverted images reasonably, the comparison should be meaningful enough.

Positive scan of two Pyrocat HD developed negatives, Shanghai GP3 100 film; left sheet processed in neutral to alkaline pH conditions, right sheet (note the clipped top left corner) processed with acidic stop and acidic fix.

Feel free to do your own comparison, but I don’t see any meaningful differences here. Now, these negatives are pretty dense, which was a conscious decision. I gave ample exposure given the nature of the mostly backlit scene and the intention to capture a wide range of tones for this processing comparison, and I also gave ample development in order to magnify any differences and to get some decent dye staining to work with. The penalty for this is that both sheets have a fair amount of dichroic fog, although this wouldn’t be problematic in regular silver gelatin or alt. process printing. Looking at the negatives, I’d say these would work nicely as salted paper prints or carbon transfer prints, so they’re pretty long-scaled negatives.

To make the comparison a bit easier to digest, let’s invert the negatives digitally and set the rebate to pure black, preserving just the image information and let that occupy the full tonal scale of the digital image. In other words: invert and using levels, set the black point to the dmin of the rebate, without further curve adjustments.

Inverted, rebate set to black, no curve adjustment. Acid-processed negative to right.

I still see no meaningful difference. The only thing I’m really tempted to do, is to adjust the curve a bit to create a rendition as the negatives might be printed or displayed digitally as a final ‘work’:

A rendition as the negatives might be finished for display

For the image above, I applied a curve adjustment mostly to reduce shadow contrast and increase highlight contrast, so basically a ‘saggy’ curve. I also clipped some of the deepest shadows, although not by much: note the preservation of shadow detail in the shadow on the right-hand candle holder. I also shifted the hue and modified the chroma, using the scanned pyro stain color as the basis for the final image color. That’s a bit of a red herring, as the pyro stain is of course a tan color in the negative, so after inversion, this ends up on the blue side of the spectrum. In the image above, I turned it around on the color wheel so it ended up on the orange part again, so the final image tone has no direct relationship with any physical reality of the negative. I found it looked kind of pleasing though.

Long story short: the version above is really a creative interpretation with all kinds of subjective decisions applied to it. There are millions of ways the image could be printed or digitally manipulated to give any kind of desired look. The only value for the comparison, which is limited to begin with, is that the end result is pretty much identical for both negatives. If I’m being very generous in terms of spotting differences, I might say that there’s a very subtle hue difference in the left side of the large glass jar between both negatives. However, if I do a color picker measurement on that area, the differences I get in terms of Lab* values is too small to attribute much meaning to them. Feel free to give it a try in your image editor.

Evidently, there are some differences between the negatives. They still are distinct sheets of film, and there will be minor variations in processing and perhaps even the material itself. If I look very closely, I can spot them (an area of slight dichroic fog in a corner etc.), but they don’t align in any way with the difference between both sheets in terms of stop bath and fixer pH.

One more thing: I’ve seen several people write online about how the dye stain image of a pyro negative will be removed when the negative is toned with selenium toner. Well, that one is easy enough to test. Bleach the silver image away from one of those negatives and give it a try. This is what the dye image with all the silver removed looks like:

Pyro stain image after bleaching away the silver

This should also suffice to silence criticism of pyro developers that the stain might not be image-wise and is just an overall dichroic fog. It really is image-dependent, as evidenced by the photographed scene being clearly visible as a dye image. I proceeded to mix some Adox selenium tone at a dilution of around 1+10 and treated the negative for about 10 minutes in this toner. Here’s the result:

The same pyro stain image after selenium toning

Apart from perhaps a slight difference in camera exposure (using my phone to snap these pics), there’s just no appreciable difference and certainly not an erasure of the image.

Oh, but maybe there is something magic about Shanghai film. Alright, how about another pair? I happened to have two double dark slides loaded, the other one with two sheets of Fomapan 200, which I also exposed to the same scene. I exposed them the same as the Shanghai 100, so *really* quite liberally. Just for some variation, I tray developed these, in Pyrocat HD 2+2+100 for 4 minutes, 0 seconds initial agitation and a few seconds every 30 seconds for the remainder of the development time.

One sheet went through the same sort of acetic acid stop (30 seconds) and acidified C41 fixer (3 minutes 30 seconds) as the previous Shanghai sheet. The other, control sheet received a 30 second water ‘stop’ bath, followed by a 3 minute 30 second fix in ca. 100cc. water with a teaspoon of ammonium thiosulfate and a pinch of sodium sulfite added to it, which constitutes a fairly neutral pH fix. Here is a side-by-side scan of both these sheets of film:

Another acid vs. neutral test, this time on Fomapan 200, liberally exposed and developed. Acid-stop & fixed sheet to the right, neutral pH processed sheet to the left.

The negatives are pretty bulletproof, which is by design, as I wanted to maximize the stain image so we could do that dye image comparison I hinted at earlier. The scan above shows the same pattern as the Shanghai film example: no meaningful difference.

In conclusion, while I was already skeptical about the myths about the sensitive nature of pyro stains, I now consider them to be a debunked myth. So far, I couldn’t find any meaningful effect of trying to damage the pyro stain dyes by processing a negative in an acidic stop and fixer, nor does the stain appear to be affected in any way by treating it with selenium toner. I did not go so far as to throw anything particularly nasty at these film sheets (dichromate did come to mind, I admit) because that’s not what I set out to do – I merely wanted to figure out if it’s counterproductive to use an acidic stop and/or fixer with a developer like Pyrocat. I’d say it really isn’t. Just use any old B&W fixer on your stained negatives, regardless of their acidity. The stain will be just fine regardless.

PS: a little bonus, just because it’s fun. How about a print made from just the dye stain image? I took the acid-stopped & fixed Shanghai negative from the first pair, on which I had bleached out the silver image, and printed it as a classic cyanotype:

Cyanotype print made from just a pyro-stain image, no silver involved.

Still here? Haven’t had enough yet? Alright, here’s one more: pretty much at the same time when I was doing the experiments outlined above, Andrew O’Neill did virtually the same – just with different film and both 510-Pyro and Pyrocat-HD as developers. That is to say, he tested if using Ilford Rapid Fix (an acid fixer) impacts the stain, and if there selenium toning does the same (and many other things!) Here are his findings:

Be sure to subscribe to his channel!

4 thoughts on “To stain, or not to stain – Acid and pyro developers”

  1. Hi,
    nice test. I have two questions:
    1. pH of 1% metafisulfete solution – 4,6 – isn’t it too acidic?
    2. doesn’t bleached non-pyro negative look like bleached pyro negative? I think its not pyro-stain, what remains visible..

    1. 1: I don’t think so. Besides, it’s a moot point since whatever acidity you throw at pyro stain, it doesn’t make a difference. It’s not just my tests that demonstrate this, but others, too.
      2: No, a bleached non-pyro negative is completely blank. What’s shown here, is the actual pyro stain, in this care from pyrocatechol. I would encourage you to set up a series of experiments of your own to verify this; please let me know what comes out, as another data point may come in handy to convince the really (really!) stubborn skeptics 😉 In case you’re wondering if the remaining image is for instance chromium-based (due to the chrome bleach), try a strong ferricyanide + bromide bleach followed by fixing. You’ll get the same result.

      1. Hi,
        Im not sceptic in the matter of the pyro-stain, my objections are methodological:
        ad 1 – you processed one negative in alkaline environment, second in acid – OK! But at the same end you put both negatives in acidic metabisulphite bath – it destroys whole experiment.
        ad 2 – there is nothing like completely blank negative, except for unexposed or undeveloped and fixed negative. Some residual image is always present and it doesn’t matter which developer was used. Is it stain? Residual silver? Silver iodide? Bromide? Dye? Some byproducts? I don’t know, but it’s present. Maybe not so pronounced like on “pyro” negatives, but it’s there.

        1. > you put both negatives in acidic metabisulphite bath – it destroys whole experiment.
          The common lore would have been that the acid environment would have destroyed the dye image. It’s still there.

          > there is nothing like completely blank negative
          Yes, there is. Don’t just take my word for it, though. Here’s a strip of a few negatives, probably some old Fomapan 400 or so developed in a non-staining developer (probably Mytol). They’ve been lingering in a corner of my darkroom, and just to illustrate this for you, I dropped some of the bleach I used for this blog post (I saved it) across two negatives, rinsed it off, then dropped some rapid fixer on there. The result is totally blank film with even the base+fog significantly reduced because all silver is gone. No trace of an image whatsoever. Here it is:

          Your comments on the nature of this supposedly remaining image that’s not a dye stain are rather odd – bromide would not remain as such, since it’s an ion, and if it were present as the element, it would have been gaseous and diffused away. Silver iodide (not really present in significant amounts in B&W film to begin with) would have fixed out – as it indeed did. Residual silver would have bleached out – as it indeed did. Dye: yes, it’s a dye stain image. It’s a pyro stain, remember.

          As demonstrated in the blog post, I could make a cyanotype from just the remaining dye image, suggesting that it’s not just some faint artefact, but a strong image of significant density. Its color and (lack of) chemical response furthermore all point towards it being a dye stain.

          I’m sorry, but I must disagree with your objections that seem far-fetched, ill-informed and confused in various ways.

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