Church - Table of Contents
Ascension Stained Glass Window
First Presbyterian Church
One Symphony Circle,
In the Allentown Local
Presbyterian Church - Official Web Sites
||Ford Company of
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.
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
6-panel Ascension ... Details
below: the three top panels, the bottom three panels:
Special thanks to Church
Manager Christina Trachtenberg for her
cooperation in 2010, and also to Ann Palmer for sharing her research on
the stained glass process in 2018.
Photos © 2010 Chuck
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