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Home | Articles | Hands-On: Replication of Historic Stained Glass

When restoring historic stained glass windows, every effort is made to retain and mend the original glass. However, if a piece is missing or shattered beyond repair, a new one is created using the same techniques that have been followed for centuries. Since no two window breaks have the same set of circumstances, each requires its own assessment in regard to treatment.

The case study here illustrates repairs to one of a number of vandalized windows at the historic Blessed Sacrament Church in Jamaica Plain, Massachusetts. With funding assistance from Historic Boston, Inc., the damaged windows, which date back to the church’s construction in 1913, were fully restored and releaded.

This window depicts a young Jesus in the temple with the elders. Rocks thrown through the window destroyed several sections of glass, one of which was a crucial piece depicting one of the elder’s faces. Since the glass piece was missing, other faces in the window served as models for its recreation.The following images illustrate the process of replicating the missing piece, one of the many steps involved in restoring the window to its former glory.

Step 1: A rubbing of the window made prior to disassembly documents the window’s lead lines and indicates where glass needs to be mended or replaced. For the elder’s face, a piece of tinted glass similar in color to the original is selected from our studio’s large glass “library.”
Step 2: A line is drawn on the glass to indicate the outline to be cut, which is then scored with a glass cutter. The glass is then broken apart by hand; sometimes separation is aided by first tapping the glass with the round end of the glass cutter.

Step 3: Working on a light table, preliminary outlines for the elder’s face, referred to as “trace” lines, are painted on the glass using a vitreous paint in an oil medium. Other mediums such as water and vinegar can be mixed with the pigments to allow for layering techniques and to create different aesthetic effects.

Step 4: After the trace paint lines dry, a silver stain (a processed powdered silver compound in a water medium) is applied on the back of the glass where yellow coloration is desired. Upon firing, a chemical reaction alters the color of the glass, producing amber tones where the stain was added. The silver stain technique was considered revolutionary when discovered approximately six centuries ago because of the many artistic possibilities it offered. The process allows the glass to retain a transparency ideal for painted images such as faces or attire; other tonal qualities are achieved when silver stain is applied to different colored glass.
Step 5: After this first phase of painting, the glass is placed in a kiln and fired to permanently fuse the trace lines to the glass and achieve the chemical reaction from the silver stain. A small piece of glass is sometimes added to the kiln to serve as an additional temperature gauge during the slow, but intense, heating and cooling phases. The glass shard, which is placed on a support, will start to bend when it reaches the molten state, indicating that the painted piece has reached the point necessary for the fusing and chemical reaction to occur.

Step 6: Once the firing has been completed, a second phase of painting begins using a ground glass paint mixed with water and gum arabic. This is called the “matting” process. A large brush is first used to spread paint evenly over the surface of the glass to prepare for more detailed work. In this instance, iron oxide provides the reddish brown color, whereas other compounds can produce black or gray tones.
Step 7: A variety of brushes and other tools are then used for the stippled textures and highlights that recreate the dramatic modeling and shadows seen in the original window.

Step 8: After a second firing in the kiln, the elder’s face is ready to be joined with the original remaining fragment that contains his beard. This section, broken in several pieces, was mended with epoxy applied along the broken edges. The rough outer edges are then cut to fit the curved shape of the new glass.

Step 9: The elder’s face and beard are joined together using the copperfoil mending method. This process involves using copper foil instead of lead to hold the pieces of glass together. Although a slight line remains visible, the copper foil repair method is sometimes preferred over epoxy edge gluing because it is easily reversible.

The stained glass window, now fully restored and reinstalled in the church, sparkles with brilliance. The newly created face of the elder, along with the other replicated glass pieces, blend with the rest of the window and bring new life to this antique work of art.

Brian Roche is Marketing Manager at Lyn Hovey Studio, Boston, Massachusetts, one of the country’s leading stained glass studios specializing in historic restorations and new commissions.

Joshua Hoaglund, pictured in the photographs, is the Senior Project Leader at Lyn Hovey Studio for the Blessed Sacrament Church restoration project and is responsible for all the replication work involved.

Hands-On is a feature that explores the process of handcraftsmanship through step-by-step analysis.

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