We can see from the data sheet on Ilford Multigrade Paper (https://www.ilfordphoto.com/amfile/file/download/file_id/1957/product_id/743/) that the curve gets steeper with increased contrast and tonal range shrinks (as expected). Various techniques seek to maximize tonality, and I'm a fan of the split grade printing technique. Let's assume I've printed an image with the maximum tonality that I can achieve (given my artistic contrast needs, of course :-)
Now I'm going to split tone it in sepia. In the past, I've done this by trial and error to get something that I like. What my question is: is there any more scientific way of going about toning? What happens to the print's characteristic curve during toning? Can the coloration be quantified and graphed as a product of the original characteristic curve and some modifier for time in bleach and/or chemical dilution?
Just as I can look at a film characteristic curve and understand how much latitude I have to work with and (pending development) how much contrast as well...how can I have this same insight into toning?