Francisco Mingarro Martín

Petrophysical analysis of the sculptures decay at the Cathedral of Burgos, Spain

Publisher Summary The statues located on the facade known as “Fachada de Santa Maria” in the Cathedral of Burgos are sculpted on a variety of limestone (biosparite), extracted from the Hontoria quarries. This chapter describes the study conducted to compare the chemical and petrophysical differences between the two types of statues at the Cathedral of Burgos, the Kings and the Infantes. The following assays were carried out: petrographical analysis under polarized light microscopy, X-ray diffraction, chemical analysis, hydric behavior, and durability tests that included 24 freeze-thaw cycles and 20 wetting-drying cycles. The petro-physical characteristics of the statues portraying the Infantes, sculpted in the mid-14th century, are slightly different than those of the Kings from the 19th century. The limestone used for the Infantes is finer-grained than that used for the Kings. The limestone used to sculpt the Infantes is more homogeneous, uniform, and dense than that used for the Kings, which is more fragile and breakable. On account of their petrophysical characteristics and of the durability assays carried out in a climatic chamber, the Kings statues are more sensitive to decay processes derived from freeze-thaw cycles whereas, the Infantes owe their decay mainly to wetting-drying variations. The state of preservation the Kings statues were assessed using ultrasound prospecting techniques and following results were obtained: 14 % of damage corresponds to cracking, 30 % to fissures, and 30 % to decay because of loss of cohesiveness. In the Infantes, 10% of the decay corresponded to fissures and 55 % to the degradation owing to dissolution.