Drawing, Geometry and Construction: The Dome of San Carlino Alle Quattro Fontane (1634-1675) by Francesco Borromini

Drawing, Geometry and Construction: The Dome of San Carlino Alle Quattro Fontane (1634-1675) by Francesco Borromini

Marco Canciani (University of Roma Tre, Italy)
DOI: 10.4018/978-1-5225-0029-2.ch025
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The link between the design drawing to an architectural work, sometimes goes through the definition of geometric paths which establish alignments, proportions, correspondences. The comparison of the geometric construction of survey data of an architecture and design data is very important for understanding the original design idea, highlighting not only the artist's modus progettandi, but also matches, modifications or changes respect of precisely geometric paths and its building architecture. In these studies, the church of San Carlo alle Quattro Fontane in Rome, by Francesco Borromini, is an exemplar case. The project of the church, built between 1638 and 1675 and characterized by a coffered vault with an oval planimetric shape, is documented by a consistent corpus of Borromini drawings. This research, based on survey data, can allow to make new contributions to Borromini work and formulate new hypotheses regarding his construction practice.
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The scope of this study lies within the analysis of design drawings, whose background reference has been well defined by several texts, among which Docci (1987, 2009), Maestro (1992), Fraser and Henmi (1994), Mezzetti (2004), Morlacchi (2008), Arnheim (2009), and some magazines, specifically dedicated to the graphic analysis and the history of representation, as Disegnare idee e immagini, Ikhnos and DisegnareCon. This research, which has developed in recent years regards specific topics, graphical analysis of modern architectural designs, Canciani, (2003, 2009) architectural and archaeological survey methods, Canciani, et al. (2013), and Canciani, Spadafora (2014), wishes to focus on the analysis of the constructed object, through the detection and graphical analysis of the design and through the detailed study of all the drawings.

Key Terms in this Chapter

CAP: Part of the dome relative to the upper two thirds, usually free and supported by the tiburio. The vertical meridian section may vary depending on the geometry of the dome: semicircle, raised arc, polycentric trending arc, variable, depending on the position in the case of ovate domes.

Metric Check: Control set dimensions of the project according to the unit size used at the time, in the case of Borromini, corresponding to a Roman palm.

Polycentric Curve or Oval: Curve, usually symmetrical, construct through two pairs of circular arcs, one major and one minor, interconnected through four connection points. Often confused with the ellipse, the oval is determined through a very precise construction with which one can build other concentric ovals, given corresponding centers.

Dome: Type of circular or oval vault whose geometric surface is given by the rotation of a circumference around the axis. In the case of the oval, the construction is more complex, generated, for example by similar curves arranged on parallel planes and meridians which determine a series of curved tiles.

Lantern: Terminal element of the dome, on which it rests, describing the intersection, a ring with a sometimes complex, geometry. The lantern may have dimensions equal to those of the dome.

Impost: Basic curve for the definition of the dome, generated through the section of a horizontal plane with the ceiling. This curve creates the directive in the theoretical model of the surface of the dome, while the main meridian sections represent the generating curves. In constructions with a spherical dome, the plan of the impost corresponds to the maximum parallel and vertical sections, generated by meridian planes passing through the main axis, they are semicircles are equal between each other.

Executive Design: A drawing, often detailed, sometimes executed freehand but usually traced smoothly with graphical tools such as compass and square, and a graphic scale of detail shown on the left. It is often used to indicate to the workers on site, the execution methods to use for the construction of the architectural elements.

Coffers or Lacunar: Normally used to characterize the intrados of the domes, are constructed in opera, integral with the wall structure of the dome. They are in geometric characters, which are repeated regularly. In the case of San Carlino dome, the intrados is divided into 4 levels of octagons and crosses, alternating between them and 4 intermediate hexagonal levels.

Centring: Provisional opera needed to support and conform the building of arches, vaults and domes. The centrings were mounted through a frame consisting of beams of various sizes, anchored to the wall through scaffolding holes, strong enough to support the wall structure under construction.

Geometric Construction: Set of geometric signs (straight and curved lines) that allow to draw complex curves through a rigorous procedure, using the properties of main geometric figures: perpendicularity, tangency, alignment.

Tiburio: Wall structure in the shape of cylinder or prism with a polygonal base which is enclosed within the dome. Such a structure, usually integral with the first 1/3 of the dome, with its weight it allows to re-tighten the thrust of the dome in the piers of the underlying structure.

Regulator Track: Grid of lines drawn rigorously that allow to develop the design of the architectural project according to the media and correspondences sanctioned by the construction.

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