For me the holy grail of carbon printing would be a set of highly transparent process colors rather than the relatively opaque traditional choices. Truly premium watercolor hues would be far too expensive to make in quantity, and commercial varieties inevitably tend to incorporate preservatives
which cause serious problems, and don't offer an equally permanent yellow anyway. There is a way
to enclose cadmium in clear titanium, but anything to do with cadmium is now outlawed in the EU where they know how to do this. I've got a good lead on serious alternative technology, but am stuck with finding a suitable process cyan. So far, can only get there by mixing pthalo blue and green. Would like a cleaner magenta too. Custom mfg of process colors per se would be very expensive, but technologically very feasible. The problem is, that in industrial usage, opaqueness is
an asset. Don't want to divulge too much at this point, since I simply don't have time to test this
or that. Maybe after I retire I can contribute some tidbit to the carbon theme, since I love the look
of these prints and understand pigments better than most.