How stained glass is made
The six basic steps in the production of stained glass
An artist would initially make a sketch of the overall composition of a window. Then full-sized drawings for the whole window or for different sections (panels) of the window were made. These full-sized drawings are called cartoons. Generally, the shapes of the individual glass pieces, the details to be painted, and the colors of the glass were indicated on the cartoon. In the early Middle Ages these were drawn on whitewashed boards.
After the glass pieces were cut and shaped, they were painted with a pigment formed by mixing iron oxide and ground copper with powdered glass.
Pieces of glass are held together with narrow strips of lead to form a panel. These strips are referred to as “lead came.” Lead is used because it is flexible and provides the adaptability needed for fitting around the various shapes of the glass pieces.
“Glazing” is the term for assembling a panel of stained glass that can then be set into a window. After separate pieces of glass are painted and fired, they are placed in position on the cartoon and joined together with lead came to form a panel. In the Middle Ages, a combination knife and hammer was used for this process. The knife edge was used to cut the pieces of came and the hammer end was used to secure nails to the work board to hold the edges in place during assembly.
The panel is then cemented to help secure the glass within the leads and to waterproof the window. A semi-liquid cement is applied with a brush and then is covered with a layer of chalk or sawdust to absorb excess liquid. The medieval recipe for this cement is not known, though the main ingredients were probably crushed chalk and linseed oil. The panel is then scrubbed down with a dry brush until the cement only remains under the lead.