What is egg-and-dart molding?

I'm looking to restore a 100-plus-year-old home to a look true to that period. Without photos of the original interior, I'm relying on advice from friends. One of them suggested egg-and-dart moldings, but I'm not sure what that is. Can you help?
—Peter Hammond, Columbia, Md.

That classic architectural embellishment dates back to at least ancient Greece, Peter, and some experts believe it's derived from even earlier Egyptian designs. In the modern age, it shows up most often in crown molding for high-end interiors or built-in cabinets.

An egg-and-dart design is almost always along the length of an ovolo profile (a convex quarter circle or ellipse similar to quarter-round molding). Not all ovolo designs, however, have egg-and-dart features. "Eggs" (half ovals with the rounded ends down) alternate with pointed "darts" (any shape resembling arrows, anchors, or tongues). This feature can stand alone as the primary focus of a molding, shown above, or be used in conjunction with other shapes to make up a wider molding, below.