Facsimile of a sacred cave at the pre-Hispanic UNESCO World Heritage site of Risco Caído
Gran Canaria and Madrid, 2019
Working inside the main chamber of Cave No. 6 at Risco Caído © Oak Taylor Smith for Factum Arte
Factum Arte has been working with the Cabildo de Gran Canaria since early 2019 on a project to record and re-materialise an exact facsimile of ‘Cave No. 6’ – the mysterious almorragén or ‘Sanctuary’ of Risco Caído. The project is an exceptional demonstration of how new technology can serve to promote accessibility to vulnerable cultural heritage sites around the world whilst monitoring and maintaining their present condition.
Risco Caído is shorthand for a complex of troglodyte settlements in the mountains of central Gran Canaria – a prime example of the pre-Hispanic cave-dwelling cultures of the Canary Islands. The 21 artificial caves of Risco Caído, dug into the soft volcanic tuff rocks of the area, comprise cult cavities as well as spaces used for living and storage. The entire site was incorporated into the UNESCO World Heritage List in July 2019 as ‘Risco Caído and the Sacred Mountains of Gran Canaria Cultural Landscape’.
Inside the main chamber of Cave No. 6 at Risco Caído © Oak Taylor Smith for Factum Arte
The unique dome of the almorragén and the light channel © Oak Taylor Smith for Factum Arte
Cave No. 6, recorded by Factum in Spring 2019, is dominated by a unique architectural dome hewn into the surrounding rock; a remarkable "optical device" in the roof of the main chamber channels light onto one of the walls, revealing a surface heavily decorated with cup-marks, pubic symbols and other bas-reliefs. The space has been interpreted as having a sacred function related to the movement of sun and stars and is thought to be an example of a pre-historic solar calendar.
An exact facsimile of the Cave at 1:1 scale produced by Factum will be on permanent view at the new Risco Caído Interpretation Centre in the town of Artenara. To the naked eye, the facsimile will look identical to the original cave, encouraging visitors to question the real importance of an 'original' in a world in which our cultural heritage is increasingly at risk from both natural and human causes. The facsimile, easier to get to than Risco Caído, will make this fragile site more accessible to the public, assisting in its long-term preservation and raising awareness about its precarious situation.
A combination of non-contact digitisation techniques was employed to capture the colour, surface texture and dimensions of Cave No. 6.
First, a LiDAR scanner (terrestrial laser measuring system) was used to generate a precise geometrical model of the interior of the cave. The 1:1 model also functioned as a base that was later superimposed with the colour and textural data.
The most interesting textured surfaces were recorded in 3D using photogrammetry, a technique that can produce detailed 3D models by extracting common features from hundreds of overlapping 2D images. Over 2500 images were taken at Risco Caído and processed using RealityCapture software to reproduce the subtle relief of the carved rock faces. High-resolution colour was captured using panoramic photography under controlled lighting. Digital colour correction methods employed in post-processing ensured accuracy in the colour of the facsimile.
Pedro Miro setting up the LiDAR scanner © Oak Taylor Smith for Factum Arte
Measuring the main chamber using low-tech methods © Oak Taylor Smith for Factum Arte
Otto Lowe taking images to generate the high-res 3D model that provides the texture for the facsimile © Oak Taylor Smith for Factum Arte
A team of expert digital technicians, craftsmen and restorers worked on the rematerialisation of the Cave at Factum's Madrid workshops.
The digital 3D model from LiDAR and photogrammetry data was rematerialised in several pieces using CNC milling, a method that involves removing material from a surface using a series of progressively finer drill bits to obtain both the general form and subtle relief texture. The colour recorded with panoramic photography on-site was printed as a reference for the artists who worked on the recreation – they had to paint the surface of the facsimile in a lengthy and subtle process of matching colour to 3D model and reference print.
Over the past 6 months, Factum Arte's craftsmen have been working on the production of an exact facsimile of the Risco Caído cave.
The ‘negative’ or ‘mould’ of the facsimile was CNC-milled in several sections. Then, original features on the surface (such as salt efflorescence and areas with distinctive colouring) were traced onto each section. The sections were coated with latex, creating a transparent protective ‘film’ between the milled surface and the first layer of colour. This initial layer, which contained the surface details captured by the colour photography of the cave, was varnished with a coat of acrylic resin to enhance its durability.
A second layer of colour was added, mimicking the natural colour of the stone, followed by a third fiberglass layer as reinforcement. Working ‘backwards’ by adding one layer at a time, in a way similar to digital printing, resulted in a natural, accurate rendition of cave’s complex colour structure.
The outer shell of the facsimile was made using epoxy resin and glass fibre over a mesh structure. Once this support structure had been fixed to the colour layers, the entire facsimile was detached from the ‘negative’ CNC-milled sections. The initial latex coating was also removed from the surface.
The sections of the cave were assembled in the workshops, allowing Factum’s artists the opportunity to make final adjustments to the colour of the surface using the full photographic survey of the cave.
© Oak Taylor Smith for Factum Arte
© Oak Taylor Smith for Factum Arte
The facsimile was shipped in sections to Artenara, Gran Canaria, in January 2020, and reassembled in the Risco Caído Interpretation Centre, which has been carved into the mountain next to the original site.
Additional resources (in Spanish):
Factum Arte team: Pedro Miró, Otto Lowe, Juan Carlos Arias, Oak Taylor Smith, Francesco Cigognetti, Francisco Regalado, María del Carmen Pascual, Aniuska Martín Fernández, Laura Revuelto Ramírez, Manuel Campo Trueba, Amanda Blázquez Ávila, Pepe Gomez Acebo, Voula Paraskevi Natsi.