Carvajal Alcaide, Rocío

Historic treatises on stonecutting of the sixteenth and seventeenth centuries contributed to progress in the study and understanding of properties of the different surfaces and the intersections between them. One of the topics that contributed most towards the development of knowledge of the geometry of surfaces was the practical use of ruled surfaces. Defining the geometry of a piece of stone by surfaces that can be cut using a ruler as a guide and a check has always been considered very interesting in the field of stonecutting. This present study focuses on stairs in two Spanish treatises to illustrate how warped surfaces were treated.

On the eastern façade of the cathedral of Jaen, attached to the so-called Gothic wall, there is an open-well stone spiral staircase, probably built in the early years of the 16th century. In the northern area of the tower, we also find another spiral staircase, built in the first third of the 18th century, with very similar characteristics. The originality of both staircases lies in their intrados surface that presents some helicoidal grooves. There are very few built examples of this type of spiral staircase and those known so far have been linked to Mediterranean Gothic architecture. In this work we have analyzed from a geometric and constructive point of view the Gothic staircase of Jaen, as well as similar examples, especially the one located in the Lonja de la Seda of Valencia. This study of stereotomic analysis has allowed us to deepen our knowledge of the construction process of the cathedral of Jaen, establishing two clear stages in the construction of the Gothic wall and the spiral staircase. We have confirmed the direct relationship between the Valencian example and that of Jaen, confirming the theories of a transfer of knowledge between the Mediterranean area and Andalusia in the last years of the 15th century and the beginning of the 16th century.