The "white" or "clear" is steam; white when condensing; clear before - you can't see steam.
"Smoke" (unburned hydrocarbons) is never "clear"; a steam locomotive (coal or oil) produces various forms of black, near-black or even dark gray smoke, or, when the fuel and firing come together, effectively almost no smoke at all.
A "clear stack" is a combination of non-condensed steam and good combustion. But white is condensing steam, typically on a colder day, when steam transitions from a HP vapor to
LP (atmospheric) vapor.
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Great videos (both), but the model J has a rogue traction tire on the side rod.
