Splitting object using boolean difference...

…folks, I’ve been attempting to split an object (a pair of eye glasses) in two. I create a mesh plane in object mode to intersect with the location of the desired split of the glasses. I then “pick” both objects…the glasses and the plane, enable the boolean function “difference” and then get confused. I’ve chosen the object “plane” or the object “glasses” but with differing results. I know I’m missing something for I’ve had success eons ago using an old version of Blender.

Suggestions would be greatly appreciated. Walter.