Reverse Painting on Glass
A reverse painting is one that has been painted directly on the back of the glass, in reverse.  "Verre glomis", the technical term, has roots as far back as the 3rd Century AD.  I have been painting in this style for many years and recommend that it be hung on a wall not over a window in order that the light does not show through the painting.  I use acrylic paint, finish the back with black and clear acrylic sealer.  All backs are covered with paper and are wired for hanging.  I will sometimes use an old, interesting window if I can find one.  I remove the old paint and use the hardware if possible.