Conservation Lighting

Mary Frances Scott, SCHOTT GLAS, Mainz

In the right light

Independence Hall in Philadelphia, Pennsylvania, can be considered the birthplace of the United States. Historical documents which shaped the history of the new nation are displayed here, illuminated with fiber optic lighting from SCHOTT.

The Declaration of Independence, the Articles of Confederation and the Constitution of the United States were all drafted in Independence Hall in the formative years of the new nation. Together these writings represent the “essential” ideas of representative government in the US and are invaluable national documents. Although they are over 200 years old and their conservation a top priority for the National Parks Service, protecting them from the ravages of time in a hermetically sealed dark safe is not an option.

Encapsulated in Argon

Rather the documents are on display in the newly refurbished west wing of Independence Hall. In preparation for the new exhibit, the documents were cleaned and mended and then hermetically encapsulated. Since contact with oxygen leads to a variety of chemical reactions in organic materials, the documents were encapsulated in a special plastic, then in glass and then in an aluminum package filled with argon gas in order to slow down the natural deterioration process. Through a built-in port, argon can be re-introduced into the package as necessary.

Further the display case is climate controlled to keep temperature and humidity constant. There is also no heat in the cabinet since fiber optic lighting is used to illuminate the invaluable documents. The light source, or illuminator, is not in the case, rather it is located 20 feet away. The light is filtered in the illuminator to eliminate the ultraviolet and infrared part of the spectrum. Likewise, light intensity is controlled directly at the illuminator with metal screens.

Each document is illuminated by two “Light Bars” from SCHOTT Fibre Optics in Doncaster, England. Multiple points of light set off in two rows provide even lighting at low conservation levels. “Producing even lighting without shadows was a major concern and the “Light Bars” worked extremely well,” said conservator Larry Bowers of the National Parks Service. “Because of the variance between the types of paper and the amount of exposure that each document has had over the years, we lit the documents at different levels between three and five foot candles (30-50 lux) to achieve the same effect for all documents.”

Another advantage for Bowers was the low maintenance of the lighting. “There is no deterioration factor to consider with the fiber optics,” he said, “and since the illuminators are long lasting, they are user-friendly for maintenance staff.”

All the documents on display in Independence Hall are original printed copies made for distribution to delegates in the respective ratification processes. The signed hand-written originals are on display at the National Archives in Washington, D.C..