Saturday, December 18, 2010

Prismatic Glass

In the late 19th and early 20th century, before reliable sources of electric light were available, commercial storefronts almost always included high ceilings and transom panels.  While this had positive aesthetic benefit it was, like most “traditional” design, firmly rooted in the practical.  Transoms allowed more light into the dark interiors of narrow, deep, storefronts.  Merchants could better display their wares, customers could better see them, and it made for a better shopping experience.

We tend to think that “high tech” is a new concept, and that it was the folks behind LEED who suddenly discovered passive energy improvements (We also tend to act as though Duany Plyter-Zyberk invented the front porch, but that’s a different rant).  Of course, early storefront designers, without electricity to save, still employed technology to improve building design.  One of my favorite examples of science in the support of better buildings is what is called “prismatic glass.”  Simply put, prismatic glass was designed with a series of angled ribs on one face that were cast based upon a strict calculation of latitude to increase their dispersal, broadcasting more light into the interior than would be the case through plate glass.  The illustration below, from a 1923 Pittsburgh Glass catalog depicts the “Scientific Explanation of the Prism” as used by that company’s 3-Way Luxfer Pressed Prism Tiles.

Nobody makes prismatic glass anymore and salvaged, often purpled, tiles (usually 6x6” or less) seem to mostly show up in antique stores where they are sold as trivets.  For restoration work I have had success having more typical ribbed glass cut into small squares, installed in zinc channel in alternating directions, and coming pretty close to replicating the traditional “Look” of prismatic glass if not its function. This is a small sample of the idea, prepared for a project in The Dalles.  The idea might get dusted off for a White Elephant in Medford, if the numbers are right.


  1. Is there a manufacturer of ribbed glass that you have had good results with?

  2. Thanks for the question, Vince. I don't have a specific manufactured to recommend. We've used 1/8" ribbed glass, cut into squares, and then mounted in lead came with the ribs oriented inward to reduce maintenance (road dust) from collecting. I've also taken that layer and kitted with a solid single panel, sort of an in-the-field IGU type installation. I am not sure how necessary this is, but it totally eliminates the need to dust the ridges.

    1/8" ribbed glass seems to be readily available from a variety of sources. I don't even know who actually manufactured the glass, I just reviewed a sample prior to construction.