This oldtime tank car, a kit from Model Diecasting/Roundhouse, has an undercarriage colored by a chemical treatment (DipIt?), that after all these years just looks unpainted; it started out black. The AP&G also has one of this kind [GPL].
Union Tank Line Car
[Miniature Worlds —> Locomotives —> Freight Cars —> Passenger cars —> Buildings —> Scenes on the AP&G —> Next]