The six basic steps in the production of stained glass
According to Wikipedia, stained glass is a glass composition formed of pieces of glass. These can be white or coloured and can receive painted decoration.
Since the beginning of the Middle Ages, these pieces are assembled by lead profiles. This process, although still dominant today, is not the only one in use: other techniques exist, such as copper ribbon, also known as the Tiffany method.
Step 1: Cartoon
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. The picture presents the cartoon for the project “La Dame au Rubis”
Step 2: Cutting
Different colors of glass were chosen for separate parts of the design, and the outline of each piece was then painted on the surface with white lime wash. Pieces were cut into rough shapes using a dividing iron, the heated tip of which was applied to the surface of the glass, causing it to break.
The pieces were further reduced to the desired size with a grozing iron—an iron bar with a slot at each end that was used to chip away at the edges of the glass until the exact shape was created. The picture presents glass cutting for the project “Dana 01”
Step 3: Painting
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. I use as well coloured enamels.
The image on the left presents the initial phase of painting of the panel “The Singer”. Wine, urine, or vinegar was added to help apply the pigment to the glass. I restrained this list to water and vinegar. This vitreous paint ranged from brown to gray to black. Once painted, the separate pieces of glass were placed in a wood-fired oven called a kiln. The heat of the kiln causes the vitreous paint to fuse permanently to the surface of the glass. During firing, the glass particles in the paint melted and merged with the glass surface to create a range of brown and black tones.
Step 4: Lead
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.
Step 5: Glazing
“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. I used exactly the same process in my workshop. The image on the left presents the glazing process of “The Singer”.
Step 6: Cementing
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.
I use the crushed chalk from Meudon in France and linseed oil.
The panel is then scrubbed down with a dry brush until the cement only remains under the lead.