Let me start out by saying that Ilford HP5 plus was not one of my favorite films. I would much rather shoot TX or TXP, that's Kodak Tri-X in 35mm and medium format. The one and only one exception is HP5 plus in medium format or large format developed in one of a few different pyro developer formulations.
For those not familiar with pyro development it has some unique properties. It is sort of a compensating developer, meaning that it develops more in the shadows and exhausts quickly in the highlights when used in high dilutions with minimum agitation. So you can get a negative with good detail thoughout the exposure range. Negatives have a very long tonal scale. Pyro is high acutance, meaning it did not dissolve the edges of the film grain and exhibited the mackie effect to some degree (enhanced edges between areas of high contrast), sort of like an automatic unsharp mask. Last but not least the image densities were composed of both silver and dye stain. The reason I used HP5 plus with pyro was specifically for the staining characteristics that the film had relative to other films and the speed. Pyro was not really a high speed developer you could expect the films sensitivity to go down almost a stop compared with other developers.
The image staining was amazing in that it added to the acutance effects but masked the grain structure giving you a very smooth super sharp image effect. It also acted as a variable built in contrast mask as densities on the film when up the dye stain became stronger in proportion. The stain was yellow-green, it so happens that blue light on variable contrast black and white paper makes the contrast go up, filtering blue out makes the contrast go down. When printing a pyro stained negative on VC paper there was a unique and beautiful easy to print fantatically detailed highlights almost automatically. Pyro stained negatives also looked fantastic on graded papers and had characteristics the same as any negative even though they looked "thin" due to some of the image density being made up of dye stain. Pyro also had amazing tonal gradation, using my scanner and todays display technologies you are only going to see a tiny tiny representation of tones that they reproduce.
The downside of this is scanning pyro developed negatives are a bitch because they react completely differently than they do printing on paper. I have tried a few times but have given up on making them look similar to what they look like on black and white paper. If anyone out there has experience with scanning and processing pyro developed negatives I would love for you to share the recipe with me. There is no comparison, so for educational purposes here are a few shots of HP5 plus and some random 100% crops. No sharpening, blackpoint to true dmax black, that's it. As usual there are some film flatness issues when viewing at 100% as well as the reality of "depth of field" with medium format.
Shot with a Hasselblad 503CW - 80mm Zeiss CF - hand held 1/60 f4 and 1/125 f2.8. Maybe I will get around to playing around with it when I can retire, I feel confident that it has something to do with treating the the color channels differently than the greyscale as a whole and then combining them so that the stain does the same thing for the scanned image as it does for printing on black and white paper. In reality I have not shot HP5 plus or printed it in at least 3 years and probably won't unless I get a hankering to fire up a darkroom again someday. I occasionally develop some film but have not been set up for prints in about 3 years.
I guess if you can take in some of the words that I sputtered on about, convert that into some sort of visual filter, and use your imagination you may be able to get an idea of the beauty of this film and developer combination. Check out the detail in the sheer fabric that is picked up at 100%. Realize how small that is in both reality and in the full image, holy crap. Even with this crappy scan a typical sharpening would make this pop. You can sort of get a feeling for the delicate way that it handles highlights looking at this crop from the face.
I still have a couple of bricks of this stuff in the downstairs fridge. If you ever get a hankering to play with pyro I would absolutely recommed HP5 plus as the film to do it with. Start with very minimal agitations, like one inverstion ever minute. If the film hasn't changed much since that last time I shot it you will probably see a real ISO of around 200 to 250. Do not shoot this at 400 no matter what the claim of the purveyer of the development formula. I personally have never seen a pyro developer get 400 out of HP5 plus. I guess if you were to really use long development times that would make it unsuitable for printing on graded papers you might get 400 as measured in the midtones but never the shadows at Zone III.
If your lacking inspiration lately and find your digital photographic life a little too complicated grab yourself a spot meter some medim format film and one of a dozen fabulous 6x6, 6x4,5, or 6x7 systems that can be had for a song on eBay. Find a willing subject and a window and enjoy. Don't be afraid of a normal lens - this was all shot on with a "normal" 80mm and I had a gaggle of other lenses to choose from. It doesn't get much better than this. I guarantee you will have a blast, probably create some really nice images, and learn a whole lot that will carry forward to your digital life. Maybe even simplifying it in the process.
Ps I am serious about hearing from people that have got the pyro negative scanning thing in the bag. I have about 10,000 pyro negatives that I cannot bear to output digitally because my feeble attempts don't even come close to my traditional silver prints and I am not one of those people that pooh-pooh digital capture or output.