I used to see a tank car or two placarded for paint or paint related materials (1263) on BNSF's trains that travel between Barstow and Richmond, CA. They may still be on them. They only showed up occasionally and I do not see those trains much anymore. My guess is they are carrying a base that is mixed with pigments. They were UTLX 643000 and 671000 series tank cars. Here is a picture someone took of one. Titanium dioxide tank cars are fairly common on these trains.
At the Sherwin-Williams plant in San Diego, it looks like they just receive titanium dioxide by rail. Its Fernley, NV plant appears to get titanium dioxide and ship or receive something in tank cars about the same size as the paint tank cars I saw. It also appears they receive something in covered hoppers.
My guess is paint manufacturers buy the solvents from chemical or refining companies. They may do some processing but my guess is they have their suppliers make them to their specifications.
