First Presbyterian Church

MERCURY MOSAIC, so named by the silvery color of the matrix.

The actual fabrication process consisted of the small triangular glass pieces laid on a pattern, which was then covered with a sheet of gummed, or adhesive covered asbestos. The asbestos sheet was turned over and a second sheet of gummed asbestos was placed on top of the first, as to form a "sandwich." A framework was placed around the outside edge of the "sandwich" and then all was tilted up at a 60-degree angle. Molten metal was poured between the edges of the asbestos sheets and it would run down into the passages between the pieces of glass, holding them together.

Several other patents for the mosaic process indicated (1) the addition of strips of brass between the pieces of glass (for a support system); and (2) placing the asbestos on a heated "back plate," raising the temperature of the glass to eliminate thermal shock.

The materials and method of construction have been widely conjectured. In 1986, H. Weber Wilson referred to the windows as "mercury mosaic" in his book Great Glass in American Architecture. The matrix was found to be a combination of lead, tin, antimony, copper, bismuth and trace elements. Essentially lead and tin. No mercury was present in any of the tests. So although Mr. Wilson stated in his book, "workers became contaminated and production was shut down," most likely it was lead poisoning that affected the workers, not mercury poisoning.

West Transept gallery stained glass window: Ascension, by the Ford Company of Boston.
Ground level window: Resurrection, by Tillinghast Studios

6-panel Ascension ... Details below: the three top panels, the bottom three panels:

Ascension - Top panels

Top, left panel: "A' stands for Alpha [and Omega]

Top, center panel

Top, left panel: "Omega," as in [Alpha and] Omega]

Ascension - Lower panels

Lower 3 panels

Left panel: Angels holding chalice and pole with sponge used by a Roman soldier in the Crucifixion
Center panel: Christ ascending into Heaven
Right panel: Angels holding spear and Christ's crown of thorns during the Crucifixion

Lower left panel - detail: Note chalice and pole with sponge used by a Roman soldier in the Crucifixion

Lower right panel - detail: Angels holding spear and Christ's crown of thorns during the Crucifixion

Special thanks to Church Business Manager Christina Trachtenberg for her cooperation in 2010, and also to Ann Palmer for sharing her research on the stained glass process in 2018.

Studios:	Ford Company of Boston
Year installed:	1892 (Building erected 1889-91)
Style:	Mercury mosaic: 1000s of small chunks of glass set in copper foil and an amalgam of mercury, lead and tin. Soldered metal caming holds the glass in place. Note it frames, not obscures, the heads.
Ascension:	Iconography