THE RESTORATION OF DECORATED PAVING STONES FROM ‘LA SEO’ CATHEDRAL, ZARAGOZA

Abstract

In the last 10 years there has been a marked increase in interest in the conservation of historic buildings in Spain. There is still much to be done, but r~scue work has now begun on endangered buildings and those structures considered to be of greatest architectural significance. In the region of Aragon, one of the largest conservation projects is the restoration of' La Seo' Cathedral in Zaragoza. The architect responsible for the work, D. Ignacio Gracia Bernal, required the collaboration of our research team to help put together a proposal for the restoration of the paved floor of the cathedral. This stone pavement was laid in the last quarter of the eighteenth century using a geometric design of large flowers and stars in a variety of stones of different colour. When part of this pavement was lifted, many of the surviving stones were found to be in a poor state. The floor was eroded and broken, with much loss of decorative detail. The primary aim of the project was to identify the lithology of the original stone so that the surviving paving stones could be restored and the floor accurately repaired with appropriate materials. The team began by studying all relevant documentary evidence relating to the laying of the floor. The two principal archives consuited were the Cathedral Archives and the Archive of Protocol of Zaragoza; these contain the original site construction notebooks and journals (dated 1777, 1783 and 1795) listing the names of the stonemasons who carried out the work and the salaries they received. In addition, there are details of the preparation and the laying of the floo'r. Finally, in the Afios Artisticos de Zaragoza (1782-83) there is a description of the original position of the pavement but sadly no information on the source of stone used. The sampling procedure was determined by two distinct objectives: firstly, the identification of the lithology of the stone used in the pavement and, secondly, the discovery of the geologic~l source from which the stones were quarried. Sampling took into consideration physical characteristics such as texture, colour and state of preservation. Fifty-eight samples were taken from those areas illustrated and included material from the high altar (zones A, B& C), the transept (zones D to G), section V (zones H to P), section IV. (zones Q & R) and lastly section III (zones S, T & U) ..Sections I and II have no evidence of eighteenthcentury pavement. Once the sampling was complete the petrological study was undertaken, beginning with the macroscopic description of colour, texture and grain size. This was followed by. petrographic analysis using a polarising microscope in which the characterization and differentiation was based on mineralogical composition and texture. Photomicrographs were taken of each thin-section to facilitate comparison between samples. To determine the source of the stone the fragments were compared with an extensive collection of rock samples from a wide variety of quarries. in Spain known to have been used in the past. This collection also includes samples of marbles, breccias, limestones and other ornamental stones from other countries (Portugal, Italy, France, Belgium, North Africa, Greece, Turkey, amongst others). The materials used in the pavement of 'La Seo' Cathedral are stones laid in geometric designs based on patterns with specific colours: black, yellow, white and red. The lithogical types determined by petrological study are listed in the following table.