Let’s take a lesson in window terminology, shall we? Windows are wooden frames for glass that are carefully fit into window openings by skilled carpenters. Every window has a top and a bottom, as well as two sides; and each part has a name. The bottom, of course, is the windowsill; the top, the window crosshead. While the windowsill is an interior fixture, the window crosshead is visible both on the interior and exterior walls. An apron is a piece of wide trim that will conceal any difference in size between the assembled window and the opening in the wall. Usually, the apron is wide with trim at its upper and lower edges, while the window crosshead is assembled from flat and quarter-round pieces. A sash window will have two glass panes that slide up and down between the sill and the crosshead. Some windows are designed with mullions, which are the upright or vertical, and crosswise or horizontal panels that form a division between units of window glass; mullions may be either functional or decorative. Once the window is fully assembled and installed, the crossheads and aprons will be the most visible decorative elements. For that reason, both may be enhanced with carefully selected and skillfully applied trim. This trim may be formed of natural woods such as pine, or it may be cast in urethane that is lightweight, holds paint from one year to the next, as well as resists rotting, cracking, water damage, warping, and insect damage. Architectural details such as window crossheads are particularly significant in colonial, Georgian, or other eighteenth-century Atlantic styles. In such interiors, windows and doors are commonly placed in symmetrical arrangement with regard to one another, so window and door crossheads will be coordinated to lend a finished look.