Historic Reflections

By Timothy Kerner, AIA 

Down a brick alleyway off the 300 block of Chestnut Street stands Carpenters’ Hall. The building’s restrained appearance belies its historic importance. The First Continental Congress convened here in 1774 to determine a response to Britain’s oppressive trade policies. The royal authorities were not pleased by the results and subsequent events only deepened their displeasure. Today, 120,000 visitors tour the Hall annually, and the issue that generates the most questions is not Colonial politics, but the waviness of the window glass.  

The typical response — the glass is wavy because the windows are handmade — barely scratches the surface. In fact, two historic wave patterns are observable in the windowpanes — parallel and concentric — and each pattern reflects a different manufacturing process. These characteristics speak of changing relationships between technology, commerce, and architecture on the eve of revolution. 

GLASS BEFORE STYLE 

Robert Smith, the preeminent Scottish master builder, was responsible for the design and construction of Carpenters’ Hall. Foundations were laid in 1770, and construction was completed four years later. The Hall displays the characteristics of the Georgian style, including compositional symmetry, classical proportions, and Renaissance-inspired details. These features convey aspirations for social harmony and the large windows reflect Enlightenment ideals of clarity and reason.  

The origins of this style can be traced back two hundred years to Andrea Palladio. His buildings constructed during the Venetian Republic of the 1500s, such as Villa Rotonda (see Figure 2), exerted a lasting influence on western architecture. The mathematically conceived forms express order and grace, and abundant natural light illuminates the interior frescoes. The quality of this light would not have been possible without the Venetian invention of clear glass.  

Stained glass windows had been used in buildings for centuries but clear glass had been an elusive quest. Venetian glassmakers devised a complex method to produce high-quality, colorless glass in 1450. The process involved converting the ashes of marsh plants into manganese dioxide, which counteracted the discoloration caused by impurities in the sand. The Venetians staunchly guarded this secret for over a hundred years, which granted them a virtual monopoly on the production and sale of clear glass and mirrors in Europe. 

Glassmakers from Venice and France were lured to England in the late 1500s. Subsequently, the English government banned the import of glass from Venice to promote domestic production. The 1674 invention of lead glass, which possessed exceptional clarity and brilliance, allowed England to surpass Venice and become the leader in European glass, exporting mirrors and clear glass across the continent and the colonies.  

Architect Inigo Jones introduced the Palladian style to England in the early 1600s. He had studied Palladio’s work during his Italian travels, and his classically inspired buildings with large, symmetrically distributed windows, were widely influential throughout Britain and the colonies. As in Venice during the prior century, this expression of clarity and enlightenment was enabled by the English development of clear glass technology.  

DISCS AND CYLINDERS 

English window manufacturers used the “crown” method of production, which was developed in France in the 1300s (see Figure 3). First, a glassmaker removed molten glass from the furnace and rolled or “marveled” it on the end of a blowpipe. It was then blown and worked into a bowl shape. A long rod was attached to the opposite side from the blowpipe, which was then broken off. The bowl was spun by the rod and centripetal force expanded the glass outward to form a disc, which could end up as large as five feet in diameter. The disc was then cooled and cut into windowpanes. The clearest and most expensive panes were cut from the outermost areas of the disc, which were the thinnest. At the center of the disc, where the rod was attached, was the “bull’s eye,” which was either used as a decorative element or thrown back into the fire. Concentric wave patterns were left within the glass as a vestige of the spinning process.   

The alternative “cylinder” fabrication method dates back even further: It was developed in Germany in the 11th century. Molten glass was gathered on the end of a blow pipe and inflated. The glass blower lengthened the cylinder by waving it in a trench cut into the floor. Through multiple cycles of heating, blowing, and swinging, the cylinder expanded. When it reached a sufficient size, the ends were cut off and the cylinder was allowed to cool. It was then scored lengthwise, placed in a reheating oven and unrolled into a flat sheet. The cylinder method produced larger rectangular pieces with an even thickness, but they lacked the clarity and brilliance of crown glass — the sheets lost their fire polish in the flattening ovens. Glass produced in this manner possessed straight, parallel waves. 

LOCAL CONCERNS 

In the 1700s, the English government continued to manipulate the glass market with tarriffs and prohibitions. Prior to the Revolution, most window glass used in America was imported from England.1 A nominal amount of glass was illegally imported from other countries, such as Holland, France, and Germany, but their share of the market was small.  

Several glass startups were attempted in the American colonies, but each failed within a few years. The strength of the English glass industry kept craftspeople from emigrating and skilled glass workers were difficult to find in the colonies. Additional challenges included the expense of constructing glass furnaces and the difficulty of finding refractory clays that could adequately withstand the high-temperature fires.2 

The first successful American glassworks was founded by Casper Wistar, a German immigrant who arrived in Philadelphia in 1717. After achieving prosperity as a brass button manufacturer and land speculator, Wistar turned to glass. In 1738, he provided the capital to build a glass factory and workers housing, and sponsored the immigration of four German glassmakers.  

His small industrial town, Wistarburgh, was located in present day Salem County, N.J., where he found the right kind of sand and plenty of trees to burn. The glassblowers used the cylinder method to fabricate windows, reflecting their German traditions.3 The glassworks grew over the next forty years, eventually employing sixty workers, and continued operation until the outbreak of the Revolutionary War.  

Wistar’s factory also produced the glass tubes that Benjamin Franklin used for his renowned electrical experiments. Out of concern that the British authorities would force the factory to close if they knew of its success, Franklin instructed his son, William, the governor of New Jersey, to diminish its accomplishments and report that its glass was, “very coarse Green Glass for Windows, used only in some of the Houses of the poorer Sort of People.”4 

Although his factory was 40 miles away, Wistar lived in Philadelphia where he owned a shop on Second and Market Street. He sold both his own glass and English crown glass. It is not known to what extent Franklin exaggerated the inferiority of Wistar’s glass, but in 1760, it was clearly less desirable than imported glass. At that time, Richard Wistar remarked that if he did not also stock English glass, “I Shall Not be able to serve half My Customers.”5 

GLASS AND MIRRORS 

At the beginning of 1773, Carpenters’ Hall was ready for its glass to be installed. An entry in the Company’s account book for January 4, 1773, records a payment of 13 pounds and 10 shillings to William Fisher & Son for three crates of glass.6 It is likely this was William Fisher IV, mayor of Philadelphia from 1773-1774. According to Genealogies of Pennsylvania Families, William Fisher was a merchant who imported “a great variety of articles,” including “boxes of glass.” This would have been English crown glass and concentric wave patterns indicative of the process can be found in certain panes in the Hall (see Figure 5). 

More glass was needed at the end of 1773 but the political situation had changed dramatically. The British enacted the dreaded Tea Act in May of that year and relations quickly deteriorated. The law granted a monopoly to the struggling British East India Company, and this outrage drove a Boston crowd to dump a shipload of tea into their harbor on December 16. Nine days later, in a more Quakerly fashion, a ship filled with tea was prevented from landing in Philadelphia and sent back to England with its unloaded cargo.  

An entry in the Carpenters’ account book for December 18, 1773, records that two boxes of window panes were purchased from John Elliott. Elliott and his son ran a prominent business on Walnut Street that sold the highest quality looking glasses (mirrors) and other glass products imported from England. Perhaps with forethought towards the worsening relations with England, the Elliotts had purchased a partially constructed glassworks in Kensington the previous year. According to their advertisement (see Figure 6) the factory was ready for business in 1773, and the glass windows were “as good, and cheaper, than that imported from Great Britain.” This glass would have been produced with the German cylinder method as the Kensington Glassworks was staffed with German glassmakers, some of whom had moved from the recently shuttered Stiegel Glassworks in Lancaster County.7 

The Carpenters’ Company account book does not record if they purchased domestic cylinder glass from Elliott or imported English crown glass. Events of the time suggest the former. One consideration is the patriotic spirit of Robert Smith, who died of pneumonia just a few years later after overseeing the construction of naval defenses in the freezing Delaware waters. Certainly, he would not have wanted to install the imperialist’s glass in his Hall windows. The parallel wave patterns observable in certain windowpanes support this conjecture. 

WAR AND GLASS 

The following year, the Continental Congress met in Carpenters’ Hall and declared a boycott on English products, including window glass. Their intention was to pressure the British government to repeal their burdensome taxes and tariffs. The boycott benefited Philadelphia’s two glassworks, but the benefits were fleeting. With the onset of war, workers were compelled to leave the glasshouses to join the Revolutionary troops and glass production was brought to a halt.  

Following the war, the American glass industry blossomed to meet the needs of the growing nation. Numerous glass factories were established in the early 1800s, especially in the Northeastern states.8 This expansion was fueled by the increasing population,  
improved transportation networks, and the continued unpopularity of English products. The Kensington Glass Works reopened under different owners in 1790 and continued to produce glass bottles until 1926. Wistarbugh did not revive after the war, but it sparked the growth of the southern New Jersey glass industry which continues today.   

DIFFERENT WAVES 

Currently, there are window panes in the Hall that are neither crown nor cylinder glass. Some are flat, featureless glass and some have superficial swirl patterns. The panes that fall into these two categories were mechanically produced and installed when it was not possible to purchase clear, mouthblown glass.  

This deficit was addressed in the 1980s by Bendheim Glass of New Jersey — they worked with their German partner, LambertsGlas, to produce authentic mouthblown window glass. Glassblowers in Waldsassen, Germany follow the traditional cylinder method that dates from the 1100s. When Carpenters’ Hall was renovated in 2022, this development allowed broken panes to be replaced with new, mouthblown glass. The irregularities within the new panes  reflect the processes of fabrication in use at the time of the Hall’s construction.  

Window glass is an essential aspect of a historic building’s character — reflecting cultural values and technological capabilities. The waves of movement held within the glass produce changing reflections that convey a dynamic luminescence to the façade. This movement also affects the view from within, modulating our vision in a manner that connects us with the past. We are used to looking through glass, but do not typically focus on glass itself. When we do, we find a mysterious material with a history of secrets and intrigue, and even clear glass can tell a fascinating story.  

Timothy Kerner, AIA, LEED AP is Principal of Terra Studio, adjunct professor at Tyler School of Art and Architecture and Co-Chair of the Context Editorial Board. 

Citations 

1. Gerard P. Scharfenberger “Recent Evidence for Broad Window Glass in Seventeenth- and Eighteenth-Century America,” Historical Archaeology, 2004, Vol. 38, No. 4, pp. 61. 

2. Arlene Palmer, “Glass Production in Eighteenth-Century America, The Wistarbugh Enterprise,” Winterthur Portfolio, 1976, vol. II, p. 81. 

3. Palmer, p. 83. 

4. William Franklin to Lord Hillsborough, June 14, 1768. The Archives of the State of New Jersey 1631-1800, Documents, 10: 29- 

5. Palmer, p. 83. 

6.  Carpenters’ Company Account Book, 1763-1834, p. 121. American Philosophical Society Library, https://diglib.amphilsoc.org/islandora/object/text241565obj. 

7. Jack McCarthy, “Glassmakers and Glass Manufacturing,” Encyclopedia of Greater Philadelphia,https://philadelphiaencyclopedia.org/essays/glassmakers-and-glass-manufacturing/ 

8. Warren C. Scoville, Warren C., “Growth of the American Glass Industry to 1880,” The Journal of Political Economy, September 1944. No. 3, p. 195. 

CAPTIONS: 

Figure 1: Carpenters’ Hall, Philadelphia, Robert Smith, 1774.  

PHOTO: JEFFREY TOTARO  

Figure 2: Villa Capra, “La Rotonda,” Vicenza, Andrea Palladio, 1590.  

PHOTO: MARK BESTON, WIKIPEDIA CREATIVE COMMONS  

Figure 3: Crown glass fabrication depicted in the 1765 Encyclopedia of Diderot & d’Alembert.  

PHOTO: UNIVERSITY OF MICHIGAN, HTTPS://ARTFLSRV04.UCHICAGO.EDU/IMAGES/ENCYCLOPEDIE/V27/PLATE_27_10_37.JPEG 

Figure 4: Cylinder glass being fabricated in Waldsassen, Germany.  

PHOTO: COURTESY OF BENDHEIM GLASS AND LAMBERTSGLAS 

Figure 5: Concentric waves in a Carpenters’ Hall window.  

PHOTO: COURTESY OF BENDHEIM GLASS AND LAMBERTSGLAS  

Figure 6: An advertisement in Poulson’s American Daily Advertiser, (2/8/1773) for glass fabricated in the recently constructed Glass Works in Kensington.  

PHOTO: TIMOTHY KERNER 

Figure 7: LambertsGlas cylinders entering the flattening oven. 

PHOTO: COURTESY OF BENDHEIM GLASS AND LAMBERTSGLAS