Lead strips called ‘cames' or ‘calmes' hold the pieces of glass together and, therefore, play a major structural role in the window. There is no general rule for how long lead cames last and medieval leading can often still be found in windows today. Like the glass, the leading can provide the conservator with significant information about the date of the window and techniques used. If the original leading has failed and needs to be replaced it should be carefully recorded and preserved. As the leading also contributes to the visual/aesthetic appearance of a window it is important to match the original width and profile when replacing the historical lead cames.