NASA Jet Propulsion Laboratory, California Institute of Technology

NASA space photography techniques were recently used to investigate the best means of preserving manuscript of the 16th century artist and scientist Leonardo de Vinci.

JPL scientists worked with conservators at the Los Angeles County Museum of Art to determine whether mounting techniques were causing any damage to the Codex Hammer, collection of Leonardo's illustrated notes on astronomy, water, light, mechanics, and Earth sciences, compiled between 1506 and 1508.

One method used to study the documents involved use of portable photographic system that is based on JPL- Caltech camera system for NASA's Space Telescope and the Galileo spacecraft mission to Jupiter. Another technique involved computer processing and enhancement of photographs of the documents in JPL's Image Processing Laboratory. Each method was used to assess whether current mounting and preservation techniques adequately protect old documents from environmental changes that could cause infinitesimal but permanent damage to the works.

The Codex Hammer, formerly called the Codex Leicester, was purchased by collector Armand Hammer in 1980. (Codex is classical Latin term meaning "manuscript.") The Codex, in an 18th century binding when purchased by Hammer, was unbound by conservators to better preserve the document and to permit public display of individual sheets. (The mounting method was devised at the British Museum and is used extensively at the Royal Library at Windsor Castle, England.) The 18, two-sided sheets of the Codex were encapsulated between two thin layers of Plexiglas so that both sides of each sheet may be viewed.

The goal of the mounting technique is very long- term preservation of the paper. While the encapsulation attempts to isolate the paper from contact with the surrounding atmosphere, changes in humidity, pressure, and temperature are transmitted through the walls of Plexiglas. In addition, the rough-textured paper is in some areas in direct contact with the Plexiglas.

JPL and Museum researchers simulated the mounting used for the Codex with 18th century paper. Computer image processing of photographs of the paper enabled the researchers to enlarge and examine millimeter-size areas of the paper for evidence of warping or micro-burnishing, where paper fibers rub against the Plexiglas encapsulation. While no evidence of micro-burnishing was found, researchers did see evidence that small portions of the paper had stretched or shrunk slightly. According to museum conservator James Druzik, such stretching could seriously damage old documents over time. Museum officials and the Armand Hammer Foundation prevent such damage by taking measures to protect the documents from temperature or humidity extremes in transport and during exhibition.

In other testing, researchers used camera called charge-coupled device, or CCD, to photographically study the Leonardo works. The CCD is capable of resolving scene into more than 1,000 shades of gray. By contrast, high quality film can record only 50 or fewer gray levels, and the human eye can discern about 16 shades of gray. Consequently, computer processing is required to display even small fraction of the information contained in CCD image.

Art conservators expect that in the near future, space observation and image processing techniques will find widespread use in art conservation laboratories.

The work was undertaken by JPL scientists David Glackin, Anne Bunker, Stewart A. Collins, and museum conservators Druzik, Victoria Blyth-Hill, John Gebhardt, and Chris Stavroudis. JPL work on the Codex Hammer was funded by the Los Angeles County Museum of Art through grant from the Armand Hammer Foundation. JPL is operated for NASA by Caltech.

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