Must warmtone or cooltone papers be used with warmtone/cooltone developers or can they be used with ordinary developer? Also can ordinary paper be used with warmtone or cooltone developers?
I found that while, for example, Ilford warmtone can be developed in either a warmtone or neutral tone developer it has a warmer, richer tone when developed in D-52 (~selectol) than in D-72 (~dektol). Like others have said you have to try your paper in different developers to see what you like.
I find that J&C Polywarmtone (Forte) works great in Dektol. I imagine a warmer effect would be achieved in a warmer developer, but I don't think I want that for what I am doing right now.
I used to regularly develop Forte Polywarmtone in Doculith and Maxim Muir's blue black (both very cold tone developers). I used to really like Polywarmtone's tonality but could not get over the olive cast. Both these developers cooled the paper of considerably but Doculith is a little high contrast for normal scenes. Maxim Muir's Blue Black was not a high contrast developer. Neutral papers in a cold tone developers are my current favourite.
The nice thing about warm tone papers is that they tend to respond very well to changes in developer - and to toning. As long as the paper base isn't coloured, you can make warm-tone paper be whatever you like!
I found that dilution of developer makes a pretty noticeable difference - I understand that some developers respond more than others to such variations. I have used both warm and cold/neutral tone papers in Dektol and found that the combination, plus various dilutions are capable of many different results, but overall, it seems that the paper makes the biggest difference to someone of my somewhat limited experience.