The reason you can "develop for the highlights" is that in normal use, the highlights (most dense) do not, in fact, develop to completion. Which is why we often use stop baths -- to force development to stop when we want it to. So... If you increase development time, you increase highlight density. And really exposed highlights can be developed to a very high density indeed. Way higher than you can print.Originally Posted by Steven Ruttenberg
OTOH, a two bath developer can, and most of them probably do, run to completion, sorta. But it's really running to exhaustion of the developer. A duplicate sheet of film (same exposure) developed in a single bath developer would likely continue to develop density in the highlights as you left it in the developer longer.
And stand development or "compensation" techniques do something similar -- they run to exhaustion locally. That is, the developer that's in the emulsion itself can run to exhaustion in the densest highlights because of the lack of agitation keeps fresh developer from getting in.
You could read the massive two volume Grant Haist book Modern Photographic Processing if you want (a lot of) extra credit. Not for the faint of heart. It lays out in amazing detail all that Haist learned in his decades as a research chemist at Kodak. And that man learned a whole lot, and kept amazing notes.
A better starting point might be Anchell and Troop's The Film Development Cookbook, whatever the newest edition might be. It covers the practical side of film development and is a much easier read than most of the other books out there IMHO.
That said, there are of course dozens and dozens of books on all kinds of darkroom topics. And all kinds of exposure and development systems. You just have to find the ones that work for you.
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