This was scanned in reflective mode to show the framing of the image and the notes by Dr. Black. His signature was on the paper that framed the image, and was placed between the two panes of glass that comprise the lantern slide. It would have been part of the slide from its construction. It is possible that Dr. Black may have constructed his own slides, which is implied by his having written on the papers in the middle of the glass.
When I unpacked the small box of lantern slides that had been sent with me from Northwestern, I discovered that a few of the slides had been part of the actual teaching slide collection of G. V. Black. G. V. Black is often referred to as the Father of American Dentistry, although it would be more accurate to refer to him as the father of dental research in America. Dr. Black was the Dean of the Northwestern University Dental School for many years during its formative time, when it became one of the leading dental education programs in the world.