Structural problems with plaster reliefs (continued)

Many cracks in the plaster relief elements radiated from nail holes, which suggested they were caused by the impact of nailing the elements to the murals without first drilling a pilot hole in the plaster. Internal metal armatures cast into many of the plaster reliefs helped to maintain the integrity of the damaged elements, but they also caused cracking when the metal expanded during corrosion. Conservators used a magnet to detect the iron armature causing cracks in this relief element, removed from the mural and shown from the back.
 
The Triumph of Religion