A pinnacle is an architectural ornament originally forming the cap or crown of a buttress or small turret, but afterward used on parapets at the corners of towers and in many other situations. The pinnacle looks like a small spire. In addition to adding to the loftiness and verticality of the structure, the pinnacles are very heavy and enable the flying buttresses to counteract the weight of the vaulted ceiling and roof. By adding compressive stress (a result of the pinnacle weight), the building’s load is shifted downward rather than sideways.
Finials are the topmost portion of a pinnacle, often sculpted as a leaf-like ornament with an upright stem and a cluster of crockets. Crockets are projected pieces of carved stone that decorate the sloping ridges of pinnacles. The carved shapes of these elements help move rainwater down while keeping the water from the roof or walls.
More than 75 percent of the Cathedral’s pinnacles were damaged in the 2011 earthquake as the seismic waves traveled up through the building and rotated the elegant pinnacle stones in different directions. The 12 pinnacles on the six flying buttresses on the east end were partially disassembled and set on the ground, and a core was drilled down through the pinnacle, and stainless steel rods were inserted through the center and into the four corners to reduce the potential for future rotation.
As teams gear up for Phase II of restoration, automated robotic carving will significantly reduce the time needed to carve and repair replacement pinnacles. Working from a solid block of Indiana limestone, a 15-ton robotic arm can rough cut a pinnacle in about 12 hours, which is then sent to the Cathedral’s stonemasons for finishing and fine detailing.