The following is a guest post by Professor Luis Lobo-Guerrero from the University of Groningen in the Netherlands and Meghan Hill, a preservation specialist in the Preservation Research and Testing Division (PRTD) of the Library of Congress.
[Luis]
When we look at a world map, with its seas and continents, we usually do not wonder how these ideas of global spaces came about in the age of discovery, particularly in the early sixteenth century. It was then when the American continent began to be delineated in charts and much of the land was still considered terra incognita. The circumnavigations of Magellan-Elcano charted the South Atlantic sections of the continent while large sections of the Pacific coasts, from today’s Mexico to Ecuador, had been mapped by Spanish expeditions. But the remaining section between mid-Ecuador until the end of Chile remained unknown. With the expeditions led by Francisco Pizarro from Panama between 1524 and 1529, in his quest to conquer the Incas, painful advances were made over this coast. Winds and currents were difficult to navigate and local knowledge was difficult to find.
I found myself exploring if the charting of such coasts were facilitated by interaction with indigenous navigators, like those described in an account of one of Pizarro’s vessels, which came across a convoy of oceanic sailing rafts trading along the coasts of Peru and Ecuador. To my wonderful surprise, this led me to discover the Chart of the Pacific Coast from Central America to Northern Chile, a portolan (nautical) map in the Geography and Map Division at the Library of Congress. When looking at its digitalisation online, I could immediately see that it was perhaps the earliest attempt of charting these coasts. The map, however, contained no toponymy (placenames), had no information on provenance, and the existing signature could not be identified. Perhaps it was merely a draft to a more comprehensive version I had yet to find, or perhaps practice for an aspiring cartographer that was never finished.
Upon reaching out to the Geography and Map Division, I was put in contact with the Preservation Research and Testing Division who conducted non-invasive materials analysis of the Chart in an attempt to garner any information from a map that initially looked to be an anomaly and make sense of why important details were seemingly missing.
[Meghan]
I started my analysis with multispectral imaging, a digital photographic technique which uses light beyond just the visible spectrum. I wanted to investigate the consistency of the inks and pigments used to draw the map, as it’s visibly evident the right side of the map is more pristine than the left. Though I didn’t yet know what the materials were, imaging confirmed they were the same across the parchment and the difference in quality was likely due to exposure that accelerated deterioration in certain areas, like water damage, perhaps. In addition, special processing of the multispectral images allowed me to render elements on that side of the map that were no longer legible, like the scale bar.
As Luis stated, and I knew from experience examining other portolan charts, it was extremely odd that there were no place names along the coastline. Illuminating the surface of the map from a low angle allowed me to examine the texture of the parchment and see whether placenames had previously existed and were possibly scratched off after the fact. But I found no disturbances to the parchment. The toponyms had intentionally been left out.
High-resolution images, both with multispectral imaging and a portable microscope, allowed us to understand how the Chart was mapped and understand the layering of the nautical elements. First, the yellow rhumb lines were laid down, then the red, then the green coastline, then the brown rhumb lines, and lastly the ship illustrations.
Other non-invasive scientific techniques allowed me to identify the pigments and ink. The red is a mixture of cochineal and vermilion, the green is verdigris, and the ink is iron gall.
[Luis]
This forensic-like investigation has already impacted my research and fundamental understanding of this map. I now believe, rather than a draft, the Chart focuses on navigating the treacherous waters of this area, thus the missing toponyms are inconsequential. The presence of cochineal, a red dye indigenous to the Americas, indicates sourcing of local materials and use of local knowledge in the making of the chart. A close study of the detailed ships may additionally suggest representation of the local culture, depicting a similar craft to the trading rafts one of the Pizarro expeditions encountered. I would also like to extend my gratitude to Dan Paterson and Catherine Magee of the Conservation Division for their insight on how, over its lifetime, this map may have been used as a ledger cover. Though we’re still uncertain, it would account for the striations on the back of the map, the envelope-shaped end of the map, and the pinpricks in the middle of the content. It wasn’t uncommon for parchment to be reused, though to me is astonishing anyone would think to hide this beautiful work of art.
As a researcher who normally focuses on abstract aspects of knowledge, working with colleagues such as Meghan has opened up a whole new range of possibilities for thinking about heritage material. After this collaboration with the Library of Congress, the coast is for me, indeed clear.
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