The simplest way to dress an arched window is to use a conventional curtain, and hang the curtain rod above the uppermost point of the arch. This is an unfussy, plain approach, but has the disadvantage that when the curtains are closed, the shape of the window is completely hidden. When the drapes are open, they can be held back with tiebacks to reveal the window shape. This style is a good choice for a bedroom, as it blocks out all light.
Depending on the structure of your window, you can choose to have a half curtain. For this option, the rod is hung across the window itself just below the arch. A conventional curtain is hung from the rod and covers only the lower part of the window, leaving the arched section exposed. This looks attractive and reveals the shape of the window, but does not block out all the light. It works best on windows that have a solid glazing bar below the arch so that the rod can be hung parallel to it.
Shaped Curtain Rails
Specialty curved curtain rails that mimic the shape of the dome are available. These are positioned above the archway, and the curtain is hung in the usual way. The curtain can be curved at the top, to follow the shape of the rail, or at the bottom. A curved-top curtain will hang with a level hem, whereas a straight-top curtain will hang with a curved hem. The advantage of this treatment is that it enhances the shape of the window. The disadvantages are that the rails sometimes have to be custom-made, which adds to the price, and the curtains can be difficult to make due to the problems of getting the curvature correct. The curved rails are not normally as robust as normal curtain rods, and will not carry a very heavy curtain.
Many people choose a combination of several treatments for their domed windows. For example, a half curtain could conceal the lower part of the window but then the arch itself could be dressed with a treatment of "swags and tails," or decorative drapery. Another option is to install decorative bosses in the center of the arch and to either side, and wind lightweight material around the center boss, allowing it to drape over the two outer ones. It is also possible to get specially shaped blinds to block out light, allowing any curtains to be decorative only.