Schnitzel, I was just talking in general terms. I do not work with printed inks that are used for printing electrical circuits.
Since the original poster was asking about conductivity, I was just suggesting what might be done. If the standard method for a specific ink is to measure it in the ink tank, that seems to be reasonable.
With printing electrical circuits, different inks are used. Some are conductors, others are non conductors and some are semiconductors. When testing conventional circuit boards, the measurements are done on the board. I guess for that reason it seemed logical to me that one should measure the conductivity of a printed ink on its substrate. That may be more of a test for how that ink performs when printed while the measuring of the ink in the tank might be better for just testing the ink.
There are issues between the electrical performance of the ink itself and how an ink will perform when it is printed. I have been told that printing electrical circuits with offset lithography is not so suitable because the water in the printed ink affects performance. If one looks at the printing technologies that are now being used to print electrical circuits, one sees flexo, gravure, inkjet, screen but hardly any offset. At this time, the available inks are not compatible with lithography. Maybe in the future.
I am just an interested observer in these new technologies. Being an engineer, I would tend to measure the performance of an ink in its printed condition and that is why I would suggest a direct measurement of the printed ink in some standard way.
It is an interesting field where a lot of development is taking place.