PRESERVATION TECH NOTES     HISTORIC GLASS NUMBER 2

Vault Light History

	Figure a.

Cast-iron vault lights were originally patented by Thaddeus Hyatt in 1845. As envisioned by Hyatt, the system incorporated small glass lenses set into cast-iron panels. The panels were modular, allowing for installation over large areas. Vault lights, sometimes referred to as “Hyatt Patent Lights,” became widespread through the second half of the nineteenth century, paralleling the rapid development of cast-iron architecture (see figures a and b).

Figure b.

As detailed in numerous historical trade catalogues of the time, vault lights were marketed to building owners and architects as a safe, inexpensive daylighting system that allowed for the conversion of previously “unusable” basements into “rent-earning, productive work space.” Prismatic pendant (or “saw-tooth”) lenses were often used in place of the basic lenses because the angled projections on the underside of the prism bent light rays directing them to the inner reaches of the lower levels (see figure c).

Vault lights were also widely employed in the early 1900s construction of New York City’s first subway system (see figure d). Purposefully employed by the designers of the Interborough Rapid Transit Company’s (IRT) subway, vault lights were constructed in the ceilings above the platforms to create an inviting underground space for a public unaccustomed to subterranean travel. Along with decorative amenities and the promise of rapid transit, the subway depended largely on pure, natural light to attract its riders.

With the emergence of Portland Cement as a new building material at the end of the nineteenth century, the vault lights used in the IRT subway system were constructed with round, translucent glass lenses set into reinforced concrete. The new concrete-and-glass version improved durability, waterproofing and slip-resistance while producing the same illuminating effect.

Figure c.	Figure d. (Photo courtesy New York Transit Museum Archives, Brooklyn, New York)

Concrete Vault Lights

Figure a.

Although this publication focuses on cast-iron vault lights, it is also possible to replace deteriorated or even missing historic reinforced concrete vault lights. Beginning in the early 1900s, this type of installation supplanted cast-iron panels. When three existing concrete panels in the sidewalk in front of Smith Tower in Seattle, Washington, were damaged by a construction truck, owners turned to a local concrete precaster to replicate the panels. The two inch thick, 4’ x 9’ panels dated to the first decade of the twentieth century and contained 180 Luxfer glass lights with saw-toothed prisms extending below. To cast new panels, measurements were first taken of the surviving panels and used to build a wood formwork (see figure a). Styrofoam cubes were set in the form to act as block outs for the square glass lights. A quarter inch, twisted square, steel rod was embedded in the original panels to reinforce the concrete.

	Figure b.

To obtain even greater strength in the new panels, a grid of steel reinforcing bars and standard 4” x 4” wire mesh was secured between the styrofoam blocks. Then concrete was poured into the mold. After the concrete set, workers removed it from the form and dug out the styrofoam placeholders (see figure b). New 1-3/4” square by 1” thick glass blocks with a pinkish tint to replicate the historic solarized lenses, were obtained from a local glass caster and setin the square voids with an epoxy (see figure c). Then, the panels were transported to the building site and installed with a backer rod and caulk (see figure d).

Figure c.		Figure d.

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