It was 40oC in the direct sun, too hot and too bright to head into Portugal’s Côa valley to record the open-air Paleolithic rock engravings of this World Heritage Site, so we waited until 8pm, until the temperature reached a slightly more manageable 32oC, and more importantly the sun was setting behind the steep side of the valley. Collaborating with Antonio Martinho Baptista and guided by André Santos, we were here to use Reflectance Transformation Imaging (RTI) to record some of the many hundreds of engraved rock panels along the River Côa, and to test whether RTI can unravel the superimpositions (the order of engraving) of the larger panels where up to 50 engravings of animals overly one another in a jumble of pecked lines.
Two decades ago, the Côa valley was due to be flooded by a hydro-electric dam project until an international campaign led by archaeologists prevented the completion of the dam and saved the landscape and its hundreds of unique open-air engravings from inundation. The oldest of these engravings, mostly depictions of horses, wild cattle and deer, are dated to the last Ice Age – at least 20,000 years ago – and may well be much older.
This visit is part of our Leverhulme Trust and British Academy funded project to test the efficacy of digital recording methods on rock and cave art and involves a network of imaging specialist and rock art experts from across the UK, Spain and Portugal. In addition to using RTI to try to unravel superimpositions, we are looking at whether RTI can reveal how cave paintings were made (e.g. were animals painted with brushes or with fingers, and where discs and hand stencils made with sprayed paints, were these sprayed directly from the mouth or through a bone tube?) and whether multi-spectral imaging can reveal paintings that have over time become covered and hidden by calcite growths.
Over two evenings, working until midnight, we recorded four panels of engravings and several engraved plaques in the Côa valley archaeological park. Preliminary processing of the data has shown that we can successfully and reproducibly show the later addition of very fine engravings over the more course pecked motifs, though more detailed analysis of the images will be done on our return to Southampton.
After visiting the Côa valley, we made the long drive to El Castillo cave in Cantabria, Spain, another World Heritage Site. Here, we are collaborating with Roberto Ontañón Peredo, making RTI and multi-spectral images of hand stencils and animal depictions. El Castillo cave contains the oldest dated cave paintings currently known in the world. Red dots associated with red hand stencils have been dated by U-Th dating to older than 40,800 years and we are interested in how they were made. Experiments have shown that similar patterns can be produced either by spitting pigment or by blowing across the top of a vertical hollow tube, like a modern spray-gun. Different techniques may result in different aerosol sizes and we hope to pick this up with RTI. In addition we have imaged some extremely fine engravings which have so far defeated attempts to record them using various laser scanning technologies.
We will present our findings at a workshop we have organized on the digital imaging of cave and rock art at the Museum of Altamira, Spain in September.
Marta Díaz-Guardamino, Alistair Pike, Dave Wheatley, Paul Pettitt