I model china clay trains in the west country in all eras (depending on what I feel like running) 70s BR blue diesels is a firm favourite at the moment with plenty of clay hoods!
I have a 4mm scale 00 gauge layout which I have been working on since October 2011, it's based on china clay operations in Cornwall
I also have a 16mm SM32 narrow gauge garden railway with live steam and battery locos.