Measure the walls above the windows themselves, where you want the curtain rod to sit, and subtract two inches from both measurements.
Cut lengths of one-inch PVC pipe that are equal to the measurements that you found in step 1.
Connect the pipes to one another using flexible PVC fittings. While you can also use rigid PVC elbows for this purpose, flexible PVC fittings allow you to have the exact bend that you need for your bow windows. For an extra degree of security, glue the ends of the pipes to the fittings using epoxy adhesive.
Cover the assembled curtain rod with spray primer and allow it to dry. The amount of time this takes is listed on the packaging.
Spray the primed curtain rod with black spray paint. When the paint dries, the curtain rod is ready to be used.