Rosenbach museum uses HOBO data loggers to monitor exhibit


Founded in 1954 by Dr. A.S.W. Rosenbach and his brother Philip, the Rosenbach Museum & Library in Philadelphia offers a variety of exhibits related to books and literature as well as fine and decorative arts. Among the highlights from the brothers’ collection are the only surviving copy of Benjamin Franklin’s first Poor Richard’s Almanac and James Joyce’s manuscript of Ulysses. Over time the collection has expanded, and now visitors also have the opportunity to check out selections from Bram Stoker’s 125 pages of working notes for his 1897 novel, Dracula.


Stoker’s notes, which include chapter outlines, character lists, and documentation of his research and reading on vampires and other demons, are the inspiration behind the museum’s “Dracula and Friends” exhibit, which runs from late September through early November as part of the museum’s annual Dracula Festival.

Kathy Haas, assistant curator at the Rosenbach, says that to avoid the risk of damage and to optimally preserve Stoker’s notes and all of the Rosenbach’s rare books, manuscripts, and objects, the museum must maintain specific humidity, temperature, and light levels. She explains, “Because our objects are sensitive, we try to keep things as stable as we can,” and the museum typically restricts the length of exhibits to four months in order to prevent excess exposure to light.

To expertly monitor the indoor environment, the museum’s curators install HOBO data loggers in each exhibition gallery, every storage area, and, occasionally, in display cases that contain objects on loan to the museum. Data loggers are also placed in shipping crates for objects being loaned to ensure that temperature and humidity levels remain stable during transit. Because these devices are small and portable, the HOBO loggers can be situated out of sight, without affecting visitor experience.

Haas notes that “with thousands of books and manuscripts on paper,” the relative humidity level is of great concern at the Rosenbach. With too much humidity, paper can absorb moisture, mold can develop, and book bindings can become warped.

To circumvent these potential problems, HOBO data loggers are used to measure and record relative humidity every ten minutes. The target is to maintain approximately 50% rH and if conditions deviate too significantly, staff members take actions to correct the environment. The curators also track humidity levels over time in order to identify long-term fluctuation in humidity, which can also damage museum objects.

Temperature can also significantly affect museum objects. Temperature changes can cause pieces to expand and contract and become damaged; warm temperatures also speed up the chemical processes of deterioration and decay. Haas notes that “what is ideal for objects isn’t always ideal for people,” and therefore they need to balance visitors’ comfort with the temperatures the museum objects and furnishings require.

Since the two buildings that house the Rosenbach Museum & Library are historic, maintaining required environmental conditions can be challenging. Fortunately, by using HOBO data loggers to monitor these conditions, the museum staff is able to make the changes necessary to correct or mitigate out-of-range conditions. Additionally, the Rosenbach uses its temperature and humidity data when filling out standard facility report forms, which all museums require before authorizing loans. Some of the data loggers are also equipped with light-intensity sensors so the Rosenbach’s curators can ensure that sensitive items are not exposed to more light than is recommended.

With the precise humidity, temperature, and light-intensity monitoring being conducted by HOBO data loggers and the staff of the Rosenbach Museum & Library, all of its rare treasures, including the working notes for Dracula, should continue to be well-preserved far into the future.

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