I can’t tell you how many times I have walked into a new spec house to find incorrect, or poorly designed mouldings. For some reason, many spec builders tend to think that a massive, built-up crown moulding will impress a potential home buyer driven by the “more is better” school of thought - overlooking the poor proportions or an unusual composition of mouldings. So I thought a short primer on mouldings might make a nice blog post.

The origin of mouldings lie in the desire to artistically refine the elements of construction (cornices, posts, beams, etc.) and to articulate their connection. This artistic refinement is enhanced through the way light and shade articulates a mouldings profile. The choice and sequence of moulding profiles establishes the classical grammar of mouldings. A grammar is an intellectual set of conventions that is sometimes trumped by visual composition, but even a rudimentary knowledge of these conventions can lead to beautifully detailed trimwork.

In classical work, a seemingly infinite combination of mouldings can be organized into four groups.

Terminating mouldings: profiles whose final curve is concave (the final movement is outward).

Supporting mouldings: profiles whose final curve is convex (the final movement is upward).

Separating mouldings: profiles such as the concave scotia or convex bead.

Translating mouldings: a terminating moulding turned upside down in order to mediate between offsets in vertical planes (such as baseboards).

From this simple classification, one can to understand the logic of why a terminating moulding is best suited for the top of a built-up cornice, for example. The thin tip of the concave profile of a terminating moulding is not visually able to hold much weight while the convex supporting moulding profile is (and is thus more appropriate farther down a built-up crown assembly). Further, the concave curve at the edge of a terminating moulding concentrates a sharp shadow line right at the top edge - giving a crisp punctuation, while the convex profile makes the shadow more diffuse.

Understanding a few simple conventions (along with some thought on proportion, scale, light/shadow, etc) can elevate the design of traditional mouldings and would avoid the poorly designed, hasitly installed, upside down crown assembly that I witnessed this morning.

For an in depth study of mouldings, see C. Howard Walker’s seminal text, Theory of Mouldings.