Privacy Glass at the Island School

By Madelyn McKinney and Jerielle Cartales

The Island School site, excavated by CAP in the summer of 2025, was filled to the brim with architectural debris from the schoolhouse’s destruction in the 1960s. Most of this was fairly generic: shards of plain window pane glass, a surplus of ferrous fasteners, numerous fragments of milled wood, endless chunks of concrete, and a barrage of brick. However, amidst these somewhat common, largely nondiagnostic artifact types, we found dozens of pieces of beautifully decorated window glass (Figure 1). These fragments became like tiny treasures to us, and so, after the field season ended, I (Madelyn) decided to dive into online archives to identify their pattern and origins.

Figure 1: Patterned window glass discovered at the Island School site. Scale is in centimeters.

In the field, CAP crew had hypothesized that this glass could be an example of privacy glass: a form of window glass that serves to decorate a space whilst obscuring views of it—all without limiting its ability to admit light (see Figure 2 for an example of this glass in use). This type of glass was first patented by James Hartley in 1847 as “rolled plate” glass marketed primarily for use in factory and greenhouse roofs.¹ In the late nineteenth century, the technology necessary to make this glass was refined by Chance Brothers & Co. when they introduced a “double rolled” version of figured glass using their patented “Mason and Conqueror” glass-rolling machine.² This machine essentially allowed the company to laminate glass sheets between two sets of rollers: one to smooth the glass and the other to pattern it.³ With the Mason and Conqueror machine, creating rolled plate glass was simpler than ever before, and thus this type of glass became increasingly common in the latter decades of the nineteenth century, both in Europe and the United States.

Figure 2: “Floralite” pattern glass from Hollander Speciality Glass (2025). Notice how the glass obscures the plant behind it whilst still admitting light to it!

Upon researching rolled and patterned glass, CAP’s tentative identification was quickly proven right––the glass from the Island School is indeed rolled, figured glass! Specifically, it is privacy glass in the pattern “Florentine” (Figure 3) which was first designed and produced by the Mississippi Glass Company, located in St. Louis, Missouri, in 1896.⁴ Mississippi Glass Co. marketed Florentine-patterned glass as “ornamental” and most commonly used for “partitions or screens where obscurity is desired”.⁵ According to various MGCo. glass catalogs, Florentine glass was produced in multiple colors, thicknesses, and sizes, with colorless ⅛ inch sheets appearing to be the most common form it took.^6,7,8 Our glass is slightly thicker than this, measuring approximately 3.8mm or 0.15in. 

Figure 3: Florentine figured glass and its description in MGCo.’s 1929 catalog.

While we can verify the design and thickness of the Island School’s glass, we unfortunately cannot claim with certainty when or by whom our glass was produced. 1896, the year the Florentine design was patented, is of course the earliest year our glass may have been made. However, we know from the catalogs produced by other glass companies throughout the twentieth century that Mississippi Glass Company was not the only manufacturer of this glass for long. Indeed, the first few decades of the twentieth century saw the figured glass industry expand immensely, and several other United States-based companies––Swindell Brothers Glass Co., Turner Glass Co., Pittsburgh Plate Glass Co., and more––began to also produce Florentine patterned glass.⁹ Because of this, we frustratingly cannot narrow down the origins of our glass, as we do not know exactly when it was ordered or placed within the Island School. Dating it between 1896 and 1963 (the year the Island School was torn down) is not particularly satisfying, but it’s all we’re able to say for certain at the moment. In any case, this beautiful window glass will remain cherished by CAP. If anything more can be found out about it in the future, we’ll write a sequel to this blog post. Stay tuned, and thank you for reading! 

The Mississippi Glass Co.

I (Jerielle) originally started this research hoping to learn more about the blue sheen that we can see in the glass (see Figure 1), but I was quickly distracted by MGCo’s sudden shift from bottle manufacturer to a national leader in plate glass production.

The Mississippi Glass Co (MGCo) operated from 1873 to the 1970s and started out as a major manufacturer of beer bottles.¹⁰ In 1880, they were one of four suppliers for Anheuser-Busch beer which used six million bottles in a single year, and one of two contracted to fill a 10 million bottle order in 1881.¹¹ Clearly, they were doing well! And yet, by 1884, MGCo was being marketed as a producer of skylights.¹² So when did they transition production and why?

In 1880, only three factories were producing plate glass from beginning to end, out of the 169 active glass factories.¹³ Most were producing container glass and cylinder glass (cylinder glass gets its name from being initially formed as a long cylinder before being cut and flatted into a single flat plate).¹⁴ In both cases, the glass is first blown and then pressed into shape via machine. Plate glass on the other hand is made by pouring molten glass into a mold and then rolling it out into a thick, flat sheet.¹⁵ While this reduces the amount of people required in the beginning, plate glass as used in windows requires more processing, equipment, and time and was too expensive to produce on a small scale.¹⁶ For example, the glass had to cool for 4-5 days before spending roughly 12 hours being machine-polished—it wasn’t until 1880 that plate glass was produced in America without the manufacturer taking a financial hit.¹⁷

Despite the difficulties in producing it, plate glass was not new, having come to the US in the 1830s as the demand for larger, clearer windows grew.¹⁸ It was commonly used in factories and greenhouses, as well as the Crystal Palace in London (Figure 4) which was built almost entirely from plate glass and cast iron. With the rising demand for factory and greenhouse skylights, it appears that MGCo decided to risk it all and became one of the earliest successful manufacturers of American plate glass. Just in time too, as by 1890 nearly 97% of plate glass used in America was produced domestically.¹⁹

Figure 4. The Crystal Palace in Hyde Park, London was originally built to house the 1851 Great Exhibition. Photograph by Philip Henry Delamotte (1821–1889).

Even more far-sighted, MGCo was a major producer of wire glass—plate glass with an internal wire screen. In 1892, the National Board of Underwriters declared for a building to be insured, plate-glass skylights had to either be internally reinforced with wire or netting had to be suspended underneath (Figure 5).²⁰ (Apparently, glass ceilings prone to breaking can be dangerous to the people underneath, who knew!) With only two manufactures of wire glass in the entire country²¹, MGCo clearly was ahead of their time. Of course, over time glass production became increasingly accessible to smaller companies, and MGCo eventually lost their monopoly.

It’s exciting to know that our fragments of privacy glass only exist because MGCo took a truly wild gamble and succeeded where many before had failed. I can only hope my endeavors have half as much success…

Figure 5. Wire netting hung underneath the windows and skylights at the World’s Columbian Exposition in Chicago²²

Thanks for reading!

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