These are the inner glass assembly panes for the window in one of the two hatches of a Gemini capsule. The window's outer glass assembly had a single pane and the inner glass assembly had two panes. All three panes in the right hatch window were optically ground for better resolution. Corning Glass made the panes of Vycor, which was 96% silica. These two panes are marked as being optically imperfect and were used solely for testing.
NASA transferred them to NASM in 1969.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.