I'd suggest Rodinal for the careful students, as they would see the different results from agitation and dilution quite clearly.
Alternatively, diluted print-developer (whatever you use in the lab) would certainly give a different 'look'.
Diafine might surprise them, and you can perhaps use a step-wedge or densitometer to demonstrate the actual difference in the scene-to-film tones.
And Caffenol, simply because it is so unusual for students who have possibly always thought film-photography requires a PhD in chemistry!
Which couple to choose might depend on the individual student, and on covering all the options between the group for discussion later. It might also be an idea to get the group to mix their own fixer from 'ordinary stuff' they (or you) have bought from the swimming-pool supplies shop, as sodium thiosulphate (old traditional fixer) is used for some sort of chlorine reducing purpose apparently. Have fun!
Last edited by MartinP; 05-25-2012 at 04:19 PM. Click to view previous post history.
Reason: readability etc.