Reinforcement bars, or Rebars, are highly recommended on all leaded glass windows that are used in a moving unit, such as doors. A leaded glass window is constructed with many individual pieces, and if not properly supported by a rebar, over time the force of a door closing will cause damage to the window. Initially, the solder joints will crack, then the window will start to bow, and if not addressed, the stress will eventually cause the glass to break. Rebars are also highly recommended on large panels, as this will help stabilize the window and reduce the fatigue that happens over time, which in turn also causes bowing.