History of Cartography

Portolans Charts and Renaissance Maps

4611.1 - Spectral Imaging of Historic Portolan Charts

Tuesday, July 4
2:50 PM - 3:10 PM
Location: Hoover

Using spectral imaging to assess Portolan Charts, early nautical charts, provided extensive new information about their construction and creation. The origins of the portolan chart style have been a continual source of perplexity to numerous generations of cartographic historians. Imaging tools developed for astronomical, remote sensing and medical imaging have been adapted and customized for the recovery of lost and obscured information that can be made visible on degraded cartographic manuscripts. The Library of Congress has developed this application to the preservation and analysis of cartographic materials as a powerful, non-invasive technique to provide access to enhance non-visible information in layers of registered high resolution digital images, characterize historic pigments and detect change. The spectral imaging system utilizes a 50 megapixel monochrome camera integrated with light emitting diode (LED) illumination panels over the range from 365nm to 1050nm. There is little information to indicate how portolan charts evolved, and what influenced their creation, and it is interesting that these nautical charts demonstrate a high level of accuracy, somewhat unexpected for their arrival in the latter half of the thirteenth-century. The surviving charts represent the earliest constructed, and studies give clear examples that the Mediterranean’s incorporated the use of local knowledge into these charts, and possibly, the improvement of these charts through direct use as trading horizons expanded. In the history of cartography, the invention of the portolan chart was a major revolutionary moment in the history of mapping. These early nautical charts began as working navigational tools of medieval mariners, initially made in the 1300s in Italy, Portugal and Spain; however the origin and development of the portolan chart remained shrouded in mystery. The style used to generate these charts was focused on the facilitation of navigational aids, and incorporated compass directions that created consistent arrays of grids across the entire chart. Research of a number of portolan charts covering the period 1320 to 1633 and these illustrate the overall focus of the nautical charts on the Mediterranean Sea, with one chart, possibly the first of the New World, outlining the pacific coast of Central and South America. Examinations of these Portolan charts confirmed their provenance through radiocarbon dating. One nautical chart of the Mediterranean and Black Seas, believed to be the earliest-known portolan chart of the Western Hemisphere, was prepared by a Genoese mapmaker between 1320 and 1350, while the New World chart vellum dated to ca. 1565 and shows the region from Guatemala to northern Peru, and may be the first chart to represent the Galapagos Islands. Little was known about the pigments and colorants used to create the charts. Spectral imaging can differentiate between pigments that appear visually identical in color and confirm the spectral response without the need to sample. Questions included whether colorants were commensurate with the time period and geographical location, and if different, did that give insight into trade routes, or possible later additions to the charts? For example; spectral data showed the red pigment on both the 1320 portolan chart and the 1565 Galapagos Islands matched vermillion, an opaque red pigment used since antiquity. The construction of these charts was also of great interest. Spectral imaging with a range of illumination modes revealed the presence of a “hidden circle” often referred to in relation to their construction. Mapping and layering of the chart rhumb lines indicated many went over the coastlines and toponyms, always assumed to have been added later in the construction. This paper will present in-depth analysis of how spectral imaging of the Portolans revealed similarities and differences, new hidden information and shed new light on construction and composition.

Fenella France

Chief, Preservation Research and Testing Division
Library of Congress

Dr. France is Chief of the Preservation Research and Testing Division at the Library of Congress researching non-destructive imaging techniques, and prevention of environmental degradation to collections. Her current focus is the development of spectral imaging and image processing techniques, and increasing links and access between scientific and scholarly data, developing and providing training workshops to preservation professionals. She received her Ph.D from Otago University, New Zealand. After lecturing at Otago, she was the research scientist for the Star-Spangled Banner project at the Smithsonian Institution. An international specialist on polymer aging and environmental deterioration to cultural objects, she focuses on links between mechanical properties and chemical changes from environmental damage and treatment protocols. Dr. France has worked on projects including the World Trade Centre Artifacts, Pre-Columbian mummies and textiles, the Ellis Island Immigration Museum, and lighting standards for the preservation of cultural heritage. With nearly three decades of experience, she serves on a range of standards and professional committees for cultural heritage preservation and maintains close links and collaborations with colleagues from academic, cultural, forensic and federal institutions. In February 2016 Dr. France was appointed the Council on Library and Information Resources (CLIR) Distinguished Presidential Fellow.


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Martin Davis

University Instructor
Canterbury Christ Church University

Since being awarded a first class honours degree in Geography by Canterbury Christ Church University (UK) and receiving the Clutton’s Prize for Best Geographical Dissertation (2014), Martin has worked as an Instructor at the University, delivering teaching in Cartography, GIS and European Geography, alongside his on-going PhD research into Soviet military cartography. In 2015, Martin was awarded the British Cartographic Society’s Ian Mumford Award for excellence in original cartographic research. Martin is a member of the British Cartographic Society and is Reviews Editor and Editorial Assistant of The Cartographic Journal (UK).


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4611.1 - Spectral Imaging of Historic Portolan Charts


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