As Scott suggested, I think the most revealing test would be to hold a sample of the printed form up to a small sparking Tesla coil topload and see if the sparks want to surface track on the printed portions more-so than the unprinted portions. A real easy test if one has a piece of Sonotube available; unfortunately I do not. I don't know at what voltage a Megger (Meager?) operates, but probably the closer to actual TC voltages, the better.
Using what I have, I just held a piece of 4" SDR PVC pipe with un-cleaned printing on it, to the sparks coming from my bug zapper-powered mini coil (http://www.laushaus.com/tesla/bzt_coil.htm ). I was unable to see any effect that the printing had to the sparks. However, when I drew a line with a graphite pencil on the PVC, the sparks made a very bright surface track along that line. Similar behavior when I sprayed a water mist onto the PVC, though not as bright as the graphite.
If someone has a piece of Sonotube and a small coil available, please try that?
Regards, Gary Lau
MA, USA