Larry - it's Tremendous ground powder with black powder paint mixed.
Getting 8 sets of point rodding laid was always going to be a bit of a challenge. The original plan was to thread the 1mm rod through sets of 8 way C&L brass rodding stools. The whole process turned out to be too impractical. So, some subtefuge was called for.. The rods are soldered one at a time using a temporary shim for spacing on to hollow 2.4mm brass bar. That and a brass strip are pinned to the baseboard with some brass rod that acts as a mounting spike. Then a half stool is soldered on at the end, each one just needs a strip over the top.
Just another 4 feet to complete.... but it does add that extra element to the infrastructure.
I'm tutoring the track making session at the Missenden Abbey modelling weekend - October 4th - there still might be spaces available.