Silhouette Edges

From Revit Help

“Revit Architecture can automatically apply a line style to silhouette edges. Silhouette edges are view-specific.
After you have applied silhouette edges to the model, there may be edges you do not want to display in silhouette. You can remove these lines as necessary”.

What it fails to say is that the Silhouette function does not work on all Categories. It works fantastically on Roofs, Wall, Floors, Columns, Structure, Openings, Furniture, Casework, Generic Models, and Speciality Equipment, Site Elements. It does not work on Mullions, Curtain Panels, Stairs, Railings, Ramps, Lighting Fixtures, Mechanical or Electrical items.

In the above graphic I've set the silhouette edges to Red in order to clearly see what is silhouetted.

The big pain here is Curtain Mullions and panels. So, on your elevations you have to manually go around and Silhouette the mullions.