For about five years HC-110 had been my only film developer. It was reliable and it kept for years in the bottle without losing strength. Other developers came and went over that time, Fomadon and Perceptol most recently, but I always came back to the Kodak syrup.
Then, like everyone else with a Facebook account and an interest in film photography, I started seeing 510 Pyro everywhere. It is the kind of product where the people who use it cannot stop telling you about it, which usually makes me suspicious. So I told myself I was a happy HC-110 person and got on with what I was doing.
The fence eventually got uncomfortable. I bought a bottle of 510 Pyro and ran a side by side test against HC-110. Then I drove down to London to sit with the man who makes 510 Pyro in the UK and ask him why the two developers actually behave differently. Here is what I learned, plus a bit of bonus material about what the test accidentally cost me.
A quick word about both developers
HC-110 has been Kodak’s flagship liquid concentrate black and white developer since 1962. For sixty years it had a reputation as the workhorse of the home darkroom. A single bottle of the syrup would last almost indefinitely. The original formula used a diethanolamine sulfur addition complex that gave it that famous shelf life, and as long as you kept the bottle reasonably closed it would still work the day you found it on a shelf five years later.
That changed in 2019. Kodak reformulated HC-110, partly because the German chemistry supplier Tetenal was about to go into receivership and partly because of regulatory pressure on diethanolamine. The new version is less viscous and less toxic. It has been openly described by former Kodak chemists as a different developer that happens to share a name. The shelf life is reduced and the keeping properties are not what they were. Depending on which batch you buy you might also get crystallization at the bottom of the bottle.
I mention this up front because by the time I ran this test in 2022 I was working with the new formula whether I knew it or not. James Lane would later point out that my HC-110 negatives looked a bit thin. The thin negatives were almost certainly the new formula at work. I should have seen this coming.
510 Pyro is much younger. It was formulated by an American photographer called Jay DeFehr in 2006, after a few years of work on an earlier developer called 110 Pyro. The 510 in the name refers to the original recipe, not to anything else. It is a single-bottle concentrate, used at extreme dilutions of one part to a hundred or more. The primary developing agent is pyrogallol, supported by ascorbic acid and phenidone, all sitting in a triethanolamine base. The pyrogallol is what makes it a Pyro developer and what gives it those distinctive stained negatives.
For years 510 Pyro was something you mixed yourself from raw chemicals if you wanted to try it, which limited the audience. That changed when James Lane founded Zone Imaging in 2020. James had been running a small film processing lab in London. During lockdown he started experimenting with developer chemistry and struck up a friendship with Jay DeFehr. Manufacturing 510 Pyro for the UK and beyond came next. By the time I bought my bottle, Zone Imaging had been selling it for about two years.
The Bronica test, with a focus problem in the background
I started small. A roll of Ilford FP4 through my Bronica S2A on a quiet weekend afternoon, mostly portraits of my daughter. Then back to the darkroom for development in 510 Pyro at the standard 1:100 dilution.
The results were a mixed message. The frames that came out in focus looked promising. There was a softness to the tones I had not seen from HC-110 negatives, and the highlights held detail in a way that felt different. But quite a few of the frames were not properly sharp, which was nothing to do with the developer. The Bronica had been showing focus problems for a couple of weeks and this roll confirmed it. The mirror return on an S2A is not the most subtle mechanism, and the focus screen is prone to going slightly off-square if it has been knocked. Mine had clearly been knocked.
This mattered because I was about to fly to Alaska for a month of work and I had been intending to take the Bronica. Now the Bronica was no longer a camera I could rely on. The Fuji GW690iii went into the bag instead, which is a different story and one I have written up in Part 1 of the Alaska piece and Part 2.
Back to the developer test, though. The Bronica roll had been useful for getting a feel for 510 Pyro in the tank. Now I needed a fair comparison.
The 4x5 test at St Arilda’s
The 4x5 is the easiest format to do a controlled developer comparison on. You can load eight sheets in eight holders and expose two identical frames seconds apart. Then develop them separately knowing exactly what changed between them. That kind of repeatability is much harder with a roll camera where every frame is different.
I drove out to St Arilda’s church at Oldbury-on-Severn, on the bank of the Severn estuary about ten minutes from my house. It is a small Norman church on a hill about half a mile from the village, surrounded by farmland and the river. I have shot there many times and I know how the light works around the building. With a red filter on the front of the lens to bring out the texture of an overcast sky, it would do as a controlled test subject.
The plan was simple. Eight sheets of FP4 in eight holders. Sheets one through four would be paired with sheets five through eight on identical subjects. So I would shoot one and five on the same composition, two and six on the next, three and seven on the next, four and eight on the last. Then in the darkroom I would develop sheets one through four in HC-110, and sheets five through eight in 510 Pyro. Each pair was identical from the lens out. The only variable between matched negatives was the developer.
I numbered the sheets one through four and five through eight rather than just one through eight because I would be loading them back into the tank in a changing bag and trying to feel which sheet was which under blackout conditions. Numbers grouped this way make it easier to identify the right set by touch.
The development
I mixed both developers at standard dilutions and set up the chemistry alongside the tank. The 4x5 sheets went into a Mod 54 insert inside a Paterson tank, four at a time, and got their respective treatment.
HC-110 first, at the dilution B that I had used for years. Then a rinse and refill of the tank, and the second batch of four into the same tank with 510 Pyro at 1:100. Standard times for the FP4 in each, fixed and washed normally.
When the negatives came out and hung up to dry, the difference was immediate. The HC-110 negatives looked exactly as I expected. Grey on a clear base, with the subjects properly readable through the film. The 510 Pyro negatives looked sepia. The staining property of pyrogallol turns the developed image into a brown shade that sits on top of the silver. The effect is striking the first time you see it on your own negatives. Across the four matched pairs the staining was consistent and obvious, which was the first useful confirmation that 510 Pyro was doing what it was advertised to do.
On the light table
The negatives came up to the light table once they were dry. The first observation was unmissable. The 510 Pyro stained the FP4 a warm sepia colour that ran across the whole frame. The HC-110 sheets next to them looked like ordinary black and white negatives. At a glance the 510 Pyro frames looked more dense, which might just be the stain doing its visual work rather than there being more silver image actually there. It is hard to read density on a stained negative by eye.
I scanned both sets through Negative Lab Pro, which is the standard Lightroom plugin for converting film negatives into positives. Negative Lab Pro does its own contrast and tonal work as part of the conversion, which means a side by side scan comparison is not a pure test of what was on the negative. But once both sets had been put through the same processing, the overall images looked surprisingly similar at first glance. The differences only really showed up when I went looking for them.
The first place to look was the sky. Sky is where highlight detail either survives or gets blown out, and Pyro developers are particularly well known for holding tonal information in the highlight regions. With the red filter pulling the cloud cover into more drama, the HC-110 sky was largely flat and white where the brightest sections of cloud had blown. The 510 Pyro sky in the matched frame had subtle tonal variation across the same areas. Not enormous, but present. On a portrait where the highlights are skin and not blown sky, that difference would be much more obvious.
The second place to look was the grain. Zoomed in on the scans, the difference was significant. The HC-110 grain was visible in the mid-tones and started to feel coarse. The 510 Pyro grain in the matched frame was finer and smoother. On a 4x5 negative this difference is fairly mild because the negative is so big in the first place. On a 35mm negative the same difference would be the gap between visibly grainy and clean.
What James Lane explained
After the test I drove down to see James Lane in London to ask him what was actually going on. James is the founder of Zone Imaging and the man making 510 Pyro for the UK market, and he was the obvious person to ask. We sat with the negatives on the table between us.
His first comment was that my HC-110 negatives looked a bit thin, which lined up with the 2019 reformulation story. The new formula is less aggressive than the old syrup at any given dilution. The 510 Pyro negatives, conversely, looked very slightly over-developed in James’s view. We had a small laugh about the fact that the most experienced chemist in the room had spotted everything I had done wrong in about twenty seconds.
Then he walked me through the actual chemistry. Both developers are high pH formulations, which means they work fast and produce high acutance. Neither has a sulfite buffer to slow the reaction, which is part of why they exhaust quickly and part of why grain tends to clump rather than dissolve away. Both keep well in the bottle because they use organic solvents instead of water. So far, common ground.
The pyrogallol in 510 Pyro is what makes the difference. The chemistry James described, when you strip out the jargon and the bits I had to ask him to repeat, is this. Pyrogallol does two things at once. It reduces the exposed silver halides into metallic silver, which is what every developer does and the bit that actually makes the picture. While it is doing that, an oxidation product of the pyrogallol stains the gelatine emulsion in proportion to how much development is happening. More development means more stain. The stain itself is not silver. It is a kind of fake density made of oxidised pyrogallol bound into the gelatine.
The clever bit is what the stain does to the look of the image. When we talk about film grain we are not actually looking at individual grain clumps. The grain we see is the gaps between the clumps. The stain fills in those gaps. The image looks smoother because the apparent grain is masked. The underlying detail in the silver is not lost. Less grain, no loss of resolution.
The way I ended up explaining this to myself, with apologies to anyone who knows actual chemistry, is the tarmac analogy. Building a road works in layers. The base layer is big stones for structural strength. Each layer above is finer stones filling the gaps between the layer below, until the surface is smooth. The big stones are still the structural element and still doing the heavy lifting, but the smaller stones fill the holes between them. The silver grain in a Pyro-developed negative is the big stones and the stain is the smaller stones filling in. The result is a smoother-looking image with the same underlying detail.
James was also keen to make the point that 510 Pyro is what they call proportional in its staining. The areas of the negative that received more light, and therefore developed more, take on more stain. The areas that received less light, and developed less, take on less. That is what makes the stain useful rather than just decorative. It is reinforcing the contrast that is already there in the silver image, not adding a flat sepia wash on top of everything equally.
The verdict
I would summarise it this way. 510 Pyro is genuinely a more interesting developer than HC-110, particularly for work where you want highlight separation and where grain is going to matter. Portrait work especially. The stain doing what it does on skin tones is exactly the kind of subtle effect that pays off on a printed enlargement or a close scanned negative. For 4x5 work where you have the negative real estate to print large, the smoother grain matters less, but the highlight handling still does.
HC-110 has not gone in the bin. The reformulated version is not the developer it used to be, but it still works perfectly well for general development at speed. It is cheaper than 510 Pyro per roll if you are not going to use Pyro for its highlight character. For documentary or working photography where I am putting a roll through every day or two, HC-110 is still the practical choice.
So the plan is to use 510 Pyro for portrait work and for any 4x5 work where I am specifically interested in the tonal character of the negatives. Anything else stays with HC-110. Both bottles live on the same shelf and both get used. Not a bad outcome for a developer I had been resisting trying for years.
A practical note worth flagging. 510 Pyro does not tolerate an acidic stop bath or hypo clear, because either will strip the stain back off the negative. Use a plain water stop and an alkaline or odourless fixer to keep the staining intact. If you have been using an acid stop with HC-110 you will need to change your darkroom routine when you switch.
What this test almost cost me
The Bronica went into the cupboard for a service after this test. The S2A focus screen was off and I needed to be sure of my equipment before flying out for a month. I took the Fuji GW690iii to Alaska instead. How that decision worked out is in Part 1 of the Alaska piece and what happened when I got home is in Part 2.
What I did not realise at the time, but worked out a few months later, is that the 510 Pyro test was the moment the Bronica problem became undeniable. Without that test I might have packed the S2A for Alaska and arrived with a camera I could not fully trust. Sometimes the developer test you ran to compare chemistry ends up doing something else entirely useful.
If you want to try 510 Pyro yourself, you can buy it direct from Zone Imaging or from any of their distributors. Silverprint, Process Supplies, Firstcall and Parallax Photographic all stock it in the UK. James and the team at Zone Imaging are also a genuinely nice operation to deal with, which matters in this niche of the hobby. You are buying from someone who actually makes the stuff, not from a reseller who has never opened the bottle.