How did they make glass windows in the old days?

During the medieval period, window glass was a rare luxury, often pieced together to form large enough sheets to cover openings. This technique laid the foundation for stained glass, commonly used in prominent church structures.

Techniques of Glassmaking in the Medieval Era

While glassmaking had roots in ancient times, it had fallen into disuse in Europe for centuries before the medieval era. Two main methods were employed to shape glass:

Slump Glass

The slump glass technique, known in German as schmelzeglas, involved heating a lump of glass or an arrangement of colored glass until it softened and then allowing it to slump or flow into place. This method could produce items such as plates, bowls, and cups. Sometimes intricate patterns and colors were applied to enhance their beauty.

Blown Glass

Somewhat more complex, the blown glass technique involved creating bubbles of glass that could be shaped into cylinders. These cylinders were then cut and flattened into sheets, making them perfect for windowpanes. However, this method produced glass that was uneven in thickness and texture, with occasional bubbles and color variations. Coloration was often achieved through the addition of coloring agents, usually minerals in the glass.

The Process

The creation of window glass involved several steps. A heated iron was used to cut smaller pieces from larger sheets. Glassmakers then worked with a tool called a grozing iron, a metal slot or hook for shaping the edges. The round ends from this process could either be tossed back into the furnace or joined together with lead, creating a technique known as bullseye windows. While these windows allowed light to pass through, vision through them was severely impaired.

Common Practices in Medieval Architecture

Before the widespread use of glass windows, especially outside of religious buildings, more common structures often had wooden shutters. These could be opened when conditions permitted. Another interesting practice was the use of isinglas, which were animal intestines flattened and moistened with drippings from animal fat, making them more translucent and weather-resistant.

Rare and Exquisite: Stained Glass

Stained glass, often found in grandiose church settings, presented a unique challenge. The presepe, or nativity scenes, were much in demand, highlighting the craftsmanship and artistry of these artisans. The use of coloring agents, typically minerals, allowed for vibrant and intricate designs, creating a visual feast for the eyes.

Conclusion

Medieval glass windows were a testament to the skill and artistry of the craftsmen of that era. The techniques used, such as slump glass and blown glass, laid the groundwork for modern glassmaking. This era not only saw the prevalence of stained glass in religious institutions but also the development of innovative materials and techniques that continue to inspire modern artists and architects.