This is one of FAQ's that I receive through email. I usually give short practical answer in direct emails, but I prefer to discuss more messy aspects here, hence this posting.(posted 8066 days ago)I said in recent thread that compensating formula don't work as they are supposed to be. I meant it makes only a small dent in creating a shoulder. I'm a post Panatomic-X generation who can't talk much about old emulsions except guessing from some "fossil films" that I have access to. But I feel a need for a discussion of what makes modern films modern, that is, making compensating formula ineffective to supress highlights.
When they say "improved emulsion" it usually means smaller silver halide particles with improved sensitizers and possibly other tricks on the composition and surface of the AgX's. This usually allows grain to be smaller and use less silver. It seems to develop effectively in more dilute developer possibly through better adsorption of developing agents on the AgX surface. (one usually double or triple the developping time when dilute 1+3 or 4x. this phenomenon has been explained by adsorption of developing agents, and as far as I know there is no dispute about this working hypothesis. this effect, of course, depends on the charge of the agent. HQ and PPD would have very different behavior here.)
It would be very interesting if John Hicks and others don't mind sharing their "rotary compensating factors" for many films. This is because if rotary agitation does not shorten processing time (to the same contrast) by a large factor, it indicates that the development is the limiting factor, meaning that enough chemicals are "there" and making the road wider doesn't help much. Modern films use different treatment for gelatin compared to old ones, like hardening. I don't know the details of the trick and how they affect the diffusion acrss it, but it is certainly worthwhile reverse engineering. For example, Delta 100 might use different trick on gelatin because it requires a large reduction in time with rotary agitation (John Hicks data), implying that diffusion is a bigger factor in overall rate compared to Delta 3200.
So why these films respond rather well to accutance formulae? Exhaustion of chemical agents are unlikely in many cases because compensation formulae don't do. One possible explanation is that halides released from highlight development diffuse out to adjacent midtone and shadows where development is inhibited. This is consistent with a phenomenon that increased sulfite diminish accutance effect, and that highlight is not inhibited.
A dichotomy: HP5 Plus v.s. TMX
HP5+ requires longer processing time when the developer is diluted compared to TMX. In other words, TMX is less sensitive to dilution error on the contrary to what is commonly believed. Incidentally, Tri-X is less dilution sensitive compared to HP5+. Different companies publish their data obtained for different criteria, and different developers act differently, but you can see a general trend by comparing them.
Having looked at curves by Clay Harmon (posted at Ed Buffaloe's site), pyrocatechin doesn't seem to make a big dent at least in Pyrocat-HD formula. This is partly because the film is developed to relatively lower density compared to conventional non-tanning formulae. Dilute pyrocatechin formulae and HP5+ or Delta 100 might do something. Besides that, there doesn't seem to be a lot of hope for compensating effect there.
If you want compensating effect, don't seek a trick in developer. Use films with intrinsic shoulder. If you want adjacency effect use combinations that are susceptible to bromide drag, preferrably containing little sulfite, at a great risk :-)
NOTE: What's stated above are mostly hypothetical models that I think are consistent with what's in the literature and what I observed, as well as what's previously discussed here. However, I don't know how far they can stretch to films I haven't used. I'm very interested in hearing contrasting observations.