There are three sideboards in existence known to be by Pittsburgh cabinetmakers. Undoubtedly there are more out there waiting to be discovered. One is seen in this short video. Although you can't see them in the video, this sideboard has two carved panels that sat on either side of the mirror. This carving is present on each of the three sideboards. The cabinetmakers of which are William Alexander, Henry Beares and Benjamin Montgomery. The similarities in the carved panels, especially in the Alexander and Beares sideboards are striking, so much so that during an initial inspection it can easily be concluded that the pieces came from the same shop. Another more likely possibility (since the sideboards are signed) is that a talented carver worked for a number of shops. That carver could have been Joseph Woodwell.
This particular sideboard is not known to have a signature. Unlike the other examples, this one contains some egyptian revival details including the feet and black marble in the center. It is also of an unusually large size.
The Henry Beares sideboard is on view at the Carnegie Museum of Art. The William Alexander sideboard can be see in Wendy Cooper's Book, Classical Taste in America.