Hyperspectral imaging is finding a home in so many interesting places, among them the fascinating field of cultural preservation. Conservation care professionals across academia and the museum world are tasked with learning as much as they can about the treasures under their care. These treasures range from artifacts such as vases, to paintings, documents, and maps.
In all cases the objective is to non-invasively increase the body of knowledge. Are there features that are invisible by any other means of analysis? Are there chemical pigmentation signatures on paintings that spectroscopy can ‘see?’ Are there any hidden writings that can be uncovered? Hyperspectral imaging can help conservation-care experts determine origins, dates, materials, and other characteristics useful to their work. Indeed, spectroscopy can also help improve the preservation of these treasures by uncovering evidence of similar efforts done years or decades previously. Hyperspectral imagers offer scholars, curators and conservators unique advantages:
- Enhance faded or hidden features-text/signatures
- Detect restorations and repairs via chemical signature
- Monitor and track changes of the object, or repairs and restorations
- Identify local material components for proper repair
- Assess original coloring and pigmentation
On December 9 at The Natural History Museum in London, Headwall organized and sponsored a workshop and seminar on hyperspectral imaging in the collection-care industry. Noted experts from worldwide universities, museums, and libraries came to hear about how hyperspectral imaging can help unlock hidden secrets while advancing the overall body of knowledge of the treasures under their care.
Mr. David Howell of The Bodleian Libraries spoke about building a suite of non-destructive imaging techniques. Mr. Chris Collins of The Natural History Museum spoke about assessing fading in natural history specimens. And Christina Duffy of The British Library discussed their use of multispectral imaging on the treasures under their care (including the Magna Carta!).
Setting the stage for the day was Mr. Kwok Wong, who serves as Headwall’s Senior Systems Applications Engineer. Kwok has done considerable work with The Museum of Fine Arts (MFA) in Boston, imaging a Mayan Vase and other artifacts. Kwok explained the basics behind multispectral and hyperspectral imaging and the kinds of valuable information that can be collected in a non-destructive, non-invasive manner.
Dr. Greg Bearman, a noted expert in the field of spectral/chemical imaging within the collection-care industry, discussed his impressive work to date and how the techniques can best be applied. Dr. Bearman’s examples included paintings, documents, and artifacts...with each requiring a slightly different approach depending on the spectral ranges that need to be covered.
Guests were encouraged to bring samples of their treasures for Headwall to image during the day. A few of the attendees did so, and Headwall had its VNIR (Visible/Near-Infrared) Starter Kit operational in the room. Attendees could see first-hand how the science of spectroscopy can be used to further their preservation and analytical efforts.
Most often, the collection-care industry cares most about imaging in the VNIR (380-1000nm) and SWIR (950-2500; short-wave infra-red) ranges. Imaging in the VNIR and SWIR has a number of important and interesting applications for Cultural Heritage because this type of imaging technology provides a more complete representation of the entire field of view. This is a critical distinction because true context is provided on what are typically heterogeneous objects; by comparison, point sensors can only sample discrete locations. Imaging in the VNIR has been used since the mid 1990s for texts and paintings. For texts, the application is typically content; for example, reading palimpsests and faded or damaged texts and maps. For art, the application is typically color and pigment mapping. SWIR imaging offers the possibility of chemical imaging, allowing the conservator to monitor and track chemistry changes over time.
Since little or no preparation of the document or artifact is necessary, this non-destructive spectral technique is invaluable for a wide range of conservation research relating to changes in color, chemical and substrates. Within the field of view of the Hyperspec® sensor, hyperspectral imaging provides quantitative spectral information for all wavelengths across the complete spectral range of the sensor.
The key to spectral data is calibration; well-calibrated datasets can be compared and analyzed over time and between multiple users. There is an existing and significant body of spectral analysis, classification and mapping algorithms and software available to work with spectral data. Most of this software has been developed over the last 20 years for satellite remote sensing and is easily available.
The job of the hyperspectral sensor is to collect image data and then assemble this valuable information into a ‘datacube,’ which represents a data set that includes all of the spatial and spectral information within the field of view.