Headwall Photonics Blog

Hyperspectral Takes Old Maps Into New Territory

Posted by Christopher Van Veen on Thu, Mar 26, 2015

Late in 2014, Headwall sponsored a successful event at London’s Natural History Museum. The purpose of the gathering was to introduce curators and preservationists to the advantages and capabilities of hyperspectral imaging. Professionals in this field understand that the treasures under their control...paintings, documents, and artifacts...need to be preserved using the most advanced techniques available. Preservation largely means having an excellent understanding of the chemical composition of the underlying materials used to create the treasures. And what the eye cannot see, hyperspectral imaging can.

The Bodleian Library (Oxford, UK) has been an acknowledged pioneer with respect to the use of spectral imaging technology. While newer than other imaging techniques, hyperspectral is relatively affordable and provides a wealth of image data that experts can pore through. With this data, the overall body of knowledge is exponentially increased on treasures having enormous historical prestige and significance. The identification of specific materials, inks, pigments, and substrates can help determine when (and perhaps even where) a document or artifact was created. Everything a hyperspectral sensor sees can be categorized with respect to its chemical signature, or ‘fingerprint.’ The color ‘Yellow’ resonates a certain way to the eye, but spectral imaging can discern the chemical composition of a particular ‘Yellow’ and match it to known spectral libraries. The results are clearly beneficial to the Bodleian, which is why the Library has taken great measure to partner with Headwall Photonics to implement systems geared specifically to what they'd like to see and learn.

BodleianTwo prized maps at The Bodleian...the 17th-Century Selden Map of China, and the medieval Gough Map of Britain...recently underwent precise analysis using Headwall’s hyperspectral sensor. The Gough Map in particular represents a mystery to Bodleian experts: when was it created, by whom, and why. By illuminating the map with non-invasive, non-destructive ‘cold’ lighting, the near infrared and shortwave infrared sensors collect a digital map of inks and materials. It even highlights features that were deliberately masked and others that simply faded or flaked away over time.

The Bodleian’s David Howell, an early advocate of spectral/chemical imaging and who helped spearhead Headwall’s Natural History Museum event, has been extremely pleased at the results seen thus far. In an interview with the BBC, Howell said that he was “blown away by the data that’s already coming out.” He noted that the technology first and foremost does not put the treasures at risk. The imaging illumination is non-destructive and the treasures themselves do not need to be removed from their climate-controlled premises.

Howell concluded with a plug for the promise of hyperspectral imaging technology: “Our biggest problem now is there’s just so much data to sort through to fully explore what we’ve uncovered!”

To read the BBC article on this exciting venture, click here.

Tags: hyperspectral imaging, artifacts, antiquities, Artwork, artwork preservation

Spectral Imaging Within the Collection-Care Industry

Posted by Christopher Van Veen on Mon, Dec 29, 2014

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.

spectral imaging in collection careIn 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.

 

Tags: Natural History Museum, artifacts, antiquities, Artwork, chemical imaging, artwork preservation, Museum of Fine Arts