Dating back to 1847, glass blocks were originally used as telegraph insulators. They were much smaller and thicker than structural glass blocks and were used mostly in the southeastern Untied States until eventually replaced with porcelain and other types of insulating materials. Glass building bricks were invented in Europe in the early 1900s as thin blocks of glass supported by a grid. Structural glass blocks have been manufactured in the United States since Pittsburgh-based Pittsburgh Corning began producing them in 1938. Blocks made at that time measured approximately 8 inches (20 centimeters) square by nearly 5 inches (13 centimeters) in depth, and cast a greenish tint as light transmitted through it. Today’s glass blocks can be a square foot in size, much more uniformly shaped, and available in many different sizes, textures, and colors.