“Prismatic Glass,” made obsolete by electric light in the 1930s, makes a comeback!

October 5, 2011

Prismatic glass is a specially made type of glass that was used in the early 20th century to direct sunlight into building interiors. Manufactured in tiles, the glass is flat on one side and ribbed with a pattern of sharp, saw-tooth “waves” on the other side. Thanks to this pattern, the glass acts like a giant prism. Sunlight that strikes the outside of the glass is refracted beautifully into the interior of the store.

Prismatic glass was introduced in the 1890’s – when Franklin Avery and Montezuma Fuller were conceiving the Avery Block Building. According to the U.S. Department of the Interior, “at the peak of popularity, over a dozen manufacturers offered varying tile patterns – each ‘scientifically designed’ to increase natural light levels and thereby reduce reliance upon light wells and artificial light sources. Prismatic glass tiles were used both in construction and to update existing storefronts, until changing tastes and the dominance of electricity led to their functional obsolescence by the 1930s.”*

In the drawing above, sunlight strikes the exterior side of the glass. Thanks to the prismatic pattern in the glass, the light is sprayed into the interior of the store. The drawing at right shows the prismatic glass in position above the store awning and main display window, as in the storefronts of the Avery Block Building.

Much of the original prismatic glass in the Avery Building has survived. But unfortunately, we found no prismatic glass remaining over the two northernmost stores.

We’re searching for a modern-day glass manufacturer who can replicate this 120-year-old glass. So far, in addition to some local possibilities we’ve found two out-of-state manufacturers who may be able to do the job. One is located in the Pacific Northwest; another is on the east coast. They’re preparing specimens for testing. Our fingers are crossed! We’ll need about 30 28” x 36” panels of replica glass to restore the entire bank of transom windows.

* National Park Service, U.S. Department of the Interior, Preservation Services, Preservation Tech Notes: Historic Glass Number 1, “Repair and Reproduction of Prismatic Glass Transoms”, by Chad Randl.

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