Sunlight and Glass, Pleasonton and Prisms

Sunlight and Glass, Pleasonton and Prisms


At the time of the Centennial, the blue glass work of General Augustus J. Pleasonton of Philadelphia must have seemed like old news, or no news. He had been working on his “cerulean process” since the start of the previous decade and had described it to the public, and patented it, in 1871. But it was only after the 1876 publication (in blue ink) of his book The Influence of the Blue Ray of the Sunlight and of the Blue Colour of the Sky . . . that his theory was embraced by the public, at least by those inclined to believe (as Pleasonton did, sincerely; he was not a charlatan) that sunlight filtered through panes of blue glass could cause plants and animals to flourish and to cast off disease. The fascination soon found its way into the daily newspapers, seized upon by advertisers as well as journalists. The telegraph allowed a new buzz to be heard across the country, and to be packaged with standardized news features and conjoint advertising. In February and March 1877, advertisements for the mazarine glass Pleasonton recommended (to be used as prescribed, one pane out of eight for plants, one out of two for human and other animals), as well as the standard interview with the general, and reports of near-miraculous cures, appeared in newspapers around the country.

But journalists will be journalists. (And scientists, scientists; Scientific American and Popular Science Monthly were among the journals that dismissed Pleasonton’s theories.) Even as parents wearing blue eyeglasses pushed perambulators topped with blue glass past music shops selling blue glass schottisches, newspapers and magazines from Boston to San Francisco served up blue glass jokes, puns, cartoons, parodies, and criticism. Some of the gems below were passed from newspaper to newspaper. (Very well, they are not advertisements. But clippings will get a toe in the door sooner or later.)

By the end of the year, there was little left of what the newspapers had described as a craze, mania, blindness, rage, folly, epidemic, and deception. Dr. Pancoast’s book, despite its blue text, red borders, and double cure for nervous excitement (red glass to produce it, blue to reduce it), does not seem to have generated a flutter of advertising and teasing. But chromotherapy and light therapy returned, sometimes separately, in other forms; for example, the electric light baths favored by J. H. Kellogg (there goes the sun!) and the Vita Glass (back to heliotherapy, without chromotherapy) of the 1920s and 1930s.

As the end of the century approached, the virtues of sunlight were invoked in a sober and practical spirit, as the ancient practice of daylighting was adapted to the congested business districts (and row houses) of the metropolis. (Blue light was said to calm those who lived and worked in tight spaces; daylighting improved those spaces.) Competition for frontage on popular blocks favored deep and narrow shops and offices, and the use of basements for offices and salesrooms. Illuminating spaces without direct sunlight could be costly and dangerous. Artificial light could stain merchandise with soot, or distort its appearance, and it could be bad for employees as well, causing eyestrain and clerical errors. A sound, economical, and lasting solution was offered by ingenious devices that worked like the old deck prisms on ships, to catch light from the sky, deflect it, and project and diffuse it into dark interiors―as we read in the wonderful ca. 1899 brochure of the Daylight Prism Company. (You can find the brochure, and the Pleasonton and Pancoast books, in the Internet Archive.) Lenses and prisms in various shapes were combined and enclosed in circular or rectangular frames, which were installed vertically (typically in shop fronts), horizontally (for skylights and floorlights as well as vault lights, also called pavement lights and sidewalk lights), or at an angle (for example, prism canopies). Natural light illuminated basements, subway stations, the backs of stores, and gloomy dining rooms.

The claims made for these devices had nothing of the overblown or miraculous in them, although the difficulty of cleaning and maintenance and the likelihood of leakage and glass discoloration belied the claim of permanence. They delivered practical benefits for decades, and they, too, have their successor technologies. And vault lights created marvelous patterns of light filtered into the underground through sidewalks and staircases. (After dark, they work in reverse, sending light up to the street; take an excuse to enjoy the first fifteen and a half minutes of Bell, Book and Candle and then watch as they play a passive bit part.) There are many vault lights elsewhere, for example, in Lower Manhattan, but they have nearly vanished from Philadelphia and are hard to detect in old photographs. But do look at the at the prism link below, and at the north side of Arch between Third and Fourth, for impressive vault lights at Roche Bobois and the Hoopskirt Factory, with prisms likely right next door at dane decor! (The photograph below at the left shows what might have been the impressive Harry C. Kahn clothing and furniture store on the northwest corner of Eleventh and Filbert, the current site of Crown Fried Chicken. Could that be Reading Terminal at the far left?) As for the shop fronts, there are dozens of possible installations (you can see some in my Flickr photostream,, scattered through the older parts of town. One can say at least that they resemble the ones in old advertisements. Some contain prisms; surely many others once contained prisms. Access to buildings and to business records and photographs (which contain many further, lost examples, even harder to confirm) will secure some of them.

For a real challenge, try to find a blue glass installation!

SS Pittsburgh Plate Glass Prisms


Paul S. Collins, Banvard’s Folly: Thirteen Tales of People Who Didn’t Change the World (Picador USA, 2001)

Tanya Sheehan, Doctored: The Medicine of Photography in Nineteenth-Century America (Penn State University, 2011) (Daylight Prism Brochure)

Click to access Prismatic+Glass.pdf

Title figure: MacCalla and Company, 237-39 Dock Street, 1900, detail; ca. 311 Arch Street; 52 North Second Street.



2 thoughts on “Sunlight and Glass, Pleasonton and Prisms

  1. I just re-read this post. I always it love it when I come across vault lights in the sidewalks in downtown Los Angeles… I hope they never disappear completely with new development. Sometimes people I am with have no idea what they are for!


  2. It is very good that you know what they are. Sometimes they are called manhole covers. Pretty fancy manhole covers, not that some are not fancy. As you say, many people have no idea, but here people could not explain the less mysterious sign on a famous old department store, “Hats Trimmed Free of Charge.” Wish I had discovered the older parts of Los Angeles before I moved away from California. Your posts make me feel like a stranger to most of the riches of the area. By the way, and back to vault lights, there were some fine samples recently in the excellent Word Press blog EPHEMERAL NEW YORK.


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