Mouldings are used in architecture to add embellishment to design and accentuate features in the building space. One of the most popular and visible is the crown. Although it sometimes sits below the ceiling (such as in a vaulted room), crown moulding most typically transitions the space between the vertical wall and horizontal ceiling surfaces.
There are a wide variety of crown profiles meant to blend with the architectural style of the building. Of equal importance to the profile is the size. When adding crown it's important to scale the moulding properly to the room size. Small rooms and lower ceilings generally mean using shallower profiles. Conversely, tall ceilings (over 8') and large cavernous rooms demand a much bigger profile to adequately remain in scale to the proportions.
The most difficult part of installing crown are the compound joints required at corners. Most modern miter saws make these joints easier to cut, but understanding the overall installation requirements will help the crown stay in place, especially when working with painted material. Painted mouldings, unlike natural wood, need to be caulked in for a seamless appearance. As the building moves, so will those caulked joints. To keep things intact, blocking and other adhesives may be required. The attached photos show a small sampling of both installing and fabricating custom crown moulding.