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What Happens When We Ultra-Dilute Pyrocat-HDC?
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Got it. No pictures... ever.
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The sharpness of diluted developers seems to boil down to the exhaustion of metol type vs the rather more complex action of the PQ type. Here the latter is summarized by AI, I am not qualified to review it:
On modern films, specifically tabular-grain (T-grain) emulsions like Kodak T-Max or Ilford Delta, diluted PQ (Phenidone-Hydroquinone) developers function as high-energy tools for maximizing edge definition and film speed.
Here is a breakdown of how this chemistry interacts with modern film technology:
1. The Super-Additivity Cycle
In these formulas, Phenidone and Hydroquinone work in a "super-additive" partnership. Phenidone initiates development at a very high speed, and Hydroquinone regenerates the spent Phenidone so it can continue working.
2. High-Efficiency Development on T-Grains
Modern T-grain films have flat, thin silver crystals with a high surface area.
3. Reduced Solvency and "Etched" Grain
Traditional developers contain high levels of sodium sulfite, which slightly dissolves the edges of silver grains to make them look smoother.
4. Resistance to Chemical Inhibition
As film develops, it releases bromide and iodide ions which can slow down the chemical reaction.
Summary for Modern Films
On modern films, specifically tabular-grain (T-grain) emulsions like Kodak T-Max or Ilford Delta, diluted PQ (Phenidone-Hydroquinone) developers function as high-energy tools for maximizing edge definition and film speed.
Here is a breakdown of how this chemistry interacts with modern film technology:
1. The Super-Additivity Cycle
In these formulas, Phenidone and Hydroquinone work in a "super-additive" partnership. Phenidone initiates development at a very high speed, and Hydroquinone regenerates the spent Phenidone so it can continue working.
- The Dilution Effect: By diluting the developer (e.g., 1+1 or 1+3), you limit the amount of Hydroquinone available. This forces the Phenidone to "exhaust" locally at the borders between bright and dark areas.
- Visual Result: This local exhaustion creates adjacency effects—microscopic boosts in contrast at the edges of objects—making the image appear significantly sharper to the eye.
2. High-Efficiency Development on T-Grains
Modern T-grain films have flat, thin silver crystals with a high surface area.
- Active Chemistry: Phenidone is roughly 25 times more active than traditional agents like Metol. Even when heavily diluted, it is powerful enough to fully develop these thin crystals without losing shadow detail.
- Film Speed: Unlike many high-acutance developers that require you to "sacrifice" film speed (shooting ISO 400 at ISO 200), diluted PQ developers generally maintain the full box speed or even provide a slight boost.
3. Reduced Solvency and "Etched" Grain
Traditional developers contain high levels of sodium sulfite, which slightly dissolves the edges of silver grains to make them look smoother.
- The Dilution Effect: Diluting the stock solution also dilutes the sulfite. This removes the "solvent" action.
- Visual Result: The grain is not "melted" or softened; instead, it is developed with sharp, distinct edges. On modern films, this creates a very "crisp" or "crunchy" texture where the grain itself enhances the perceived resolution of fine details.
4. Resistance to Chemical Inhibition
As film develops, it releases bromide and iodide ions which can slow down the chemical reaction.
- The PQ Advantage: Phenidone is uniquely resistant to these by-products. This is critical when using high dilutions and minimal agitation, as it prevents "bromide drag" (streaking) and ensures that the highlights don't become muddy or suppressed.
Summary for Modern Films
- Acutance: Maximum; provides a "3D" pop and high edge contrast.
- Shadows: Excellent; the best choice for maintaining detail in dark areas while seeking sharpness.
- Texture: High-definition grain that looks intentional and sharp rather than blurry.
Paper by Paul Zengerle who worked for Kodak. Not that I’m advocating for edge effects. They aren’t my thing, but the study is interesting nonetheless.
Further ultra dilution exploration, this time with Lucky SHD 100 ...
[April 2026] Piping Hot
2x3 Speed Graphic, 101mm 4.5 Ektar, Lucky SHD 100, Pyrocat-HDC, scan of silver print
[April 2026] Piping Hot
2x3 Speed Graphic, 101mm 4.5 Ektar, Lucky SHD 100, Pyrocat-HDC, scan of silver print
Nicely done Chuck!
Thanks. That was with Pyrocat-HDC 1:1:500 for an hour with agitation every 15 min after an initial 1 min agitation.
Nice!
(@koraks Another teaser 
I just finished printing some 35mm Tri-X I subjected to the aforementioned 1:1:500 60 minute EMA.
The results are surprising. I will provide print scans when they're dry, but I was mildly shocked to see the sharpness and total rendering when I made Tri-X look at detailed articulated leaves and trees and subjected it to this development regimen. Usually, I find this kind of subject breaks 35mm Tri-X and you get mush in the leaves.
Like I said, the prints have to finish washing and drying, but the results look quite promising.
This is sort of an academic test just to see how Tri-X works when abused this way. If I want best quality in woodland scenes I'd use MF or LF. Failing that, I'd use 35mm SHD 100, Fomapan 200, 100TMAX, or FP4. Still, it's an interesting exercise.
(I use this kind of exploration to force me to go out and shoot every week. Not only to I learn new things, but I occasionally get a keeper. Blind squirrel, acorn, etc.)
P.S. Next up might be SHD 100 in @Raghu Kuvempunagar 's recommended concoction of D-23 1+9+lye for a nice lingering hour or so.
I just finished printing some 35mm Tri-X I subjected to the aforementioned 1:1:500 60 minute EMA.
The results are surprising. I will provide print scans when they're dry, but I was mildly shocked to see the sharpness and total rendering when I made Tri-X look at detailed articulated leaves and trees and subjected it to this development regimen. Usually, I find this kind of subject breaks 35mm Tri-X and you get mush in the leaves.
Like I said, the prints have to finish washing and drying, but the results look quite promising.
This is sort of an academic test just to see how Tri-X works when abused this way. If I want best quality in woodland scenes I'd use MF or LF. Failing that, I'd use 35mm SHD 100, Fomapan 200, 100TMAX, or FP4. Still, it's an interesting exercise.
(I use this kind of exploration to force me to go out and shoot every week. Not only to I learn new things, but I occasionally get a keeper. Blind squirrel, acorn, etc.)
P.S. Next up might be SHD 100 in @Raghu Kuvempunagar 's recommended concoction of D-23 1+9+lye for a nice lingering hour or so.
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Suggested by me no doubt, but you're the biggest exponent of the method.
I've no doubts that it will give you very sharp negatives.Tri-X in ultra dilute Pyrocat-HDC 1:1:500 for an hour.
Nikon F2 handheld with a 50mm f/1.4 AIS Nikkor.
Scans of silver prints:
Nikon F2 handheld with a 50mm f/1.4 AIS Nikkor.
Scans of silver prints:
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