I remembered that Piccolite resins are clear so they're probably not
derived from pine stumps.
I called the distributor. The PICCO resins they sell now are
polystyrene. The distrubutor thought that they might have made PICCO
resins from coal tar in the distant past.
Polystyrene was around in 1960 and maybe 1950 but I don't think it
was around as a commercial material before WWII.
So PICCO resins may have been made from coal tar, not pine stumps,
in the distant past.
He told me they're still using the original PICCO factory in Ohio.
Anyway tank cars of coal tar might have been delivered to PICCO.