Glossy Carbon Variable Tone inkset -- 7800 version -- Internegatives
2016-08-15 by Paul Roark
I am not an alt process printer, but some had asked about the suitability of this inkset for the task. It appears from my reading that one limiting factor in the past was the density needed to fully utilize the very long scale of platinum/palladium papers. It appears a negative with a density range of 2 is needed. (Source: “The Book of Alternative Photographic Processes,” by Christopher James)
It appears in talking to the local alt process people that the Epson OEM inks can now reach this. So, no special inkset is necessarily needed. FWIW, however, the glossy carbon inkset I'm now using can also reach high densities, potentially way beyond the OEM inks. I don't have a transmission densitometer, but using a light meter to read through the film base and then also a 2 inch printed square of black, the PK plus 50% PK combined to make the 100% patch shows a 7 stop difference. That is just over 2 density units. (Please correct me if my old film days conversion is in error.)
If 7 stops/density 2 (plus change) is not enough range, an interesting thing I've found is that the 2 MK channels can be employed with a profile that uses 100% PK and 50% Mk (split into two 25% channels to keep the dot size down as much as possible). This results in a negative that shows over 9 stops of light blocking. That's about a density range of 3. The quality of the image at that point is not very good, but if spectral highlights of the image are all that is really involved, it'll probably work.
With the MK, the reflective density is not good, as the surface becomes less glossy. It only works for transmission density. Interestingly, there is enough amber base on the film at that point to hold the MK and avoid rub off without the need for a post-printing spray.
In general, the reflective measurements of density stop correlating with the transmission density when the coating become saturated. That does not, however, mean that the transmission density doesn't still increase. This holds true even when only glossy ink is used.
I've put several QTR profiles in the Zip file and have a small section of http://www.paulroark.com/BW-Info/7800-Glossy-Carbon-Variable-Tone-2016.pdf that also briefly discusses the issues. It may be that the profile I made for the Pictorico White Film is the best. That film lends itself to standard spectros and QTR approachs, and it's probably the same coating as on the clear films. As such, if I were doing internegatives with this inkset, I might start with that profile.
Paul