This weekend marked the third of the last four I have spent working on a trompe l'oeil ceiling for the study at home. The base color it was painted eight years ago is the right one, and I'm using one lighter and two darker shades to represent the highlights and shadow lines of faux ribs and beams in the coves. I have the basic rectangle filled in now, and three of the four walls have their ribs. Next weekend I'll add the last seven ribs and start figuring out what to do with the central part, i.e. how to fit the can lights into an overall architectural pattern. Probably some kind of coffering or rosettes - I'm still studying pictures of the kind of ceilings I'm trying to copy.
The above pictures show the steps in the process. The first picture has the pencilled in pattern for the three ribs to be painted (which are just barely visible). The second picture has the highlights added, the third has the lighter of the two shadow colors (I discovered a little gradation on the depth of the shadows makes a world of difference), and the last has the darker shadow color and the base color touch-ups where the ribs meet the beam (to make the ribs look slightly thinner than the beams). The thumbtacks and thread I use to get the lines straight are also shown - I found out the hard way that you can't freehand straight lines standing at the top of a ladder bending backwards.
I just love figuring out stuff like this. Jamie thinks I'm crazy. The boys don't care as long as they can play games on the computer while I'm working.