My questions are only intended to satisfy my own curiosity. A few years ago Kim Nielsen had told me that the museum had two Dahlgren boat howitzers in its collection, and that one of them (sometime in its history) had been displayed out of doors for many years where it had developed a patina, whereas the the other howitzer had a more polished appearance.
I thought that the 20-pdr rifled Dahlgren might have been one of the cannons he was talking about, but the howitzer on a field carriage (which I haven't seen, and didn't know about) that you mention must be one of the howitzers he was discussing.