I am building a model of the steam boat Armenia. It is said to have
had a Walking Beam Dunham Steam engine (40" bore and 14' stroke).
Does anyone have any information on this engine or ship? In
particular, I wonder if the engine frame would have been of wood or
iron, and if it would have been of wood, would it have been natural
or painted?

Walking beams were usually painted on colors - green, blue, red, black or yellow ochre, and some times a mixture of both (ie, the frame green, the beam black, etc.). Some appear in Bard paintings to be varnished natural wood, although this may actually be either a yellow ochre color or grained to imitate varnished wood. They were probobly striped, as the engines below (which were also painted in colors). Several layers of varnish would be needed to adequately protect the flat ground colors used at the time.

Jim