Nancy Turner, J. Paul Getty Museum, Vincent Beltran and Catherine Patterson, Getty Conservation Institute

Cumulative light exposure of illuminated manuscripts: steps towards an exhibitions policy

By virtue of their having been stored closed for centuries, manuscript codices preserve the brilliant colors and hues of the painted illuminations within. Since 1984, the Getty Museum has been committed to making accessible to the visiting public its collection of illuminated manuscripts with continuous, rotating displays in a permanent gallery, as well as through the organization of loan exhibitions and the regular lending of objects to international exhibition venues world-wide. But with the display of manuscripts comes exposure to light, and the possibility over time to induce fading of the most fugitive colorants used within these precious illuminations. To meet conservation preservation targets for these delicate objects, light levels for the display of illuminated manuscripts are kept low in galleries (50 lux) and manuscripts folio opening are rotated on a regular basis.

Balancing a continuous program of rotating exhibitions as well as supporting loans to external exhibitions can be challenging, especially given the repeated pressures to exhibit ‘masterpiece’ or foundational objects from a collection. To effectively communicate these issues to curatorial staff during the planning of internal exhibition and the evaluation of loan requests, a straightforward method of communicating exposure limits and risks for individual objects to the Getty’s manuscripts curators has been developed and employed over the past ten years. The method is a simple color-coded system based upon the concept of ‘Just Noticeable Fade’ (JNF)/’Just Noticeable Difference’ (JND) as tied to ISO-Blue Wool standards and preservation risk-assessment models for the display of light-sensitive materials (J. Ashley-Smith, J. Druzik, S. Michalski, P. Whitmore and others). In an ongoing dialogue to raise awareness with curators, this system has helped make concrete the issues of cumulative light exposure risks and fade rates in order to help set preservation targets by limiting the exposure of certain objects and by encouraging the display of alternate objects from the collection.

While the total amount of light exposure to which a manuscript/folio has been subjected prior to its entering the collection cannot be fully known, subsequent light exposure can be calculated from museum exhibition records (e.g., based on number of days on exhibit, hours illuminated per day, and gallery light levels). This information, together with Micro-Fade Testing (MFT), an accelerated micro-light exposure testing method, and Fiber-Optic Reflectance Spectroscopic (FORS) pigment analysis conducted by Getty Conservation Institute scientists, allows for predictive measurements of the fade rates of specific organic colorants. A log of display times for each manuscript, down to the folio number (or if a single leaf, its recto or verso side) is thus generated. The log is updated at the end of every gallery rotation (at the Getty Museum manuscripts are rotated on a quarterly basis) and color coded to reflect a ‘warning-light’ system (red/amber/green) established by the conservator to alert curators when a folio or leaf is nearing the preservation target for light exposure.

This talk will present this simple color-coded system, using examples drawn from the J. Paul Getty Museum’s collection of manuscripts. The fading of organic red hues in particular will be discussed as a way to effectively convey “JNF”, Blue Wool standards, and the effects of light exposure to curatorial colleagues in an effort to help set and maintain reasonable preservation targets and inform the decision-making process for the display of manuscript folios.