Ian, I had bookmarked this before and it is well worth a read and bookmark by anyone interested in colouring. What you achieved here is quite remarkable and would, I imagine, be very difficult to achieve by the normal pencils/oils approach unless you were very skilled in pencils/oils.
pentaxuser
Yes it's a very much more versatile set of techniques, essentially there's three. First the normal toning, then there can be dye coupled toning, and third there's the dye colouring using retouching dyes.
Books (1970's and earlier) suggested using masking fluid to do the selective toning but I found it better without, selectively bleaching freehand, However I did a lot of retouching and composite images, cut out work, etc, commercially so could work very quickly, plus I did a lot of research into toners. I guess I was doing this at the same time as Bob Carlos Clarke was evolving his own methods while doing an MA at The Royal College of Art. I met him after a talk around 1986 and we very briefly discussed Dye couplers.
Should have added Bob Carlos Clarke's firts two books are also worth a look at, the first was The Illustrated Delta of Venus, a selection of Anais Nin's stories and some of his photo's better is Obsessions still quite expeimental
Ian