Old glass windows were primarily made using early glassmaking techniques that involved manual labor and specific artisanal skills, with one prominent method being the crown glass process. This method, common for centuries, produced distinct window panes with unique characteristics that are still visible in historic buildings today.
The Crown Glass Method: An Early Innovation
One of the most significant early methods for producing window glass involved a process where glass was mouth blown into a hollow globe or “crown” and then hand spun into a flat disk which was then cut into the required pane sizes. This intricate technique resulted in glass panes that were both functional and aesthetically unique.
Here's a breakdown of the crown glass production steps:
- Gathering the Molten Glass: A skilled glassblower, known as a gaffer, would gather a blob of molten glass from a furnace onto the end of a long, hollow iron blowpipe.
- Blowing the Globe: The gaffer would then inflate the glass by blowing through the pipe, shaping it into a large, hollow globe or sphere, often referred to as a "crown."
- Attaching the Pontil Rod: Once the globe was formed, it was transferred from the blowpipe to a solid iron rod called a "pontil" or "punty." The pontil was attached to the opposite side of the globe from where the blowpipe was removed. This left a distinctive circular mark, known as a "bullseye," on the finished disk.
- Spinning into a Disk: The glass globe, still hot and pliable, was then rapidly spun by hand. The centrifugal force caused the glass to flatten out into a large, thin disk, typically several feet in diameter. As it spun, the glass would cool and stiffen.
- Cooling and Cutting: After the disk had fully flattened and cooled, it was carefully detached from the pontil rod. The large glass disk was then cut into smaller, rectangular or square panes suitable for windows. The quality and clarity of these panes varied depending on their position within the original disk.
Characteristics of Crown Glass Panes
Crown glass panes are easily recognizable by certain tell-tale signs resulting from their unique manufacturing process.
| Characteristic | Description |
|---|---|
| Bullseye | The central point where the pontil rod was attached, often thicker and less clear. |
| Swirls & Ripples | Circular or wavy distortions and inconsistencies caused by the spinning motion. |
| Varying Thickness | Panes tend to be thicker towards the center of the original disk and thinner towards the edges. |
| Limited Size | Due to the spinning method, individual panes were often smaller than those produced by later methods. |
These imperfections, far from being defects, are cherished by historians and architects as hallmarks of authenticity and craftsmanship. They contribute to the charming, undulating appearance often associated with antique window glass.
Legacy and Evolution
The crown glass method was a dominant technique for centuries, from the late Middle Ages into the 19th century, particularly in England and France. It was eventually superseded by more efficient and less labor-intensive processes, such as the cylinder method (broad sheet) and later, the float glass process, which allowed for the production of larger, flatter, and more consistent sheets of glass. Nevertheless, the crown glass method remains a foundational part of glassmaking history, demonstrating the ingenuity and skill of early artisans.
