Over the years, I have repaired a number of stained glass pieces, from smallish panels to large entryway ones.  Repairs are oftentimes far more difficult than constructing a panel from the beginning.  If they are in a window frame, they have to be removed, putty dug out, stops removed, and then the really hard work begins.  Depending on the age of a piece, the lead may be oxidized, stretched, broken or missing, and if this is extensive, it's often better to reconstruct the whole piece.  If the glass gods are kind, there may be only a few pieces broken around the perimeters, but all too often, they are not kind.  Cracked glass all too often is found right in the middle.

A pattern is made by rubbing a pencil's lead over the panel while it is laid flat, a process similar to grave rubbing.  Piece by piece, the panel will be disassembled, all the pieces cleaned to remove years of dirt and then the process is reversed, using the rubbing made in the beginning.  This is the somewhat easier part of the process, as it is like building a panel from start.  Once releaded, all joints soldered, pieces puttied or cemented, the panel is inserted back into the window frame.