|
Cultural heritage materials are often fragile, unique and have little documentation about their history and hence what is best for their preservation. Challenges of cultural heritage materials therefore necessitate a focus on non-invasive analytical techniques with a large component of the investigation being a forensic-like approach to recreate the history of use, the impact of various environmental parameters and provenance. The results of these analyses are then used to determine degradation mechanisms and how best to preserve these historic items for future generations. Cultural heritage materials include a range of material types and go from antiquity to yesterday – historic and modern polymers, paper and parchment as substrates, inks and colorants and the media used to capture and record our history, photographic processes. Other collections include glass, metal, wood, ceramics, textiles, magnetic tape, wax cylinders and other sound and storage media. Paper and parchments are prepared and manufactured in many different ways with different sizings, trace metals that can become corrosive at specific levels in both papers and pigments, pigments having a range of binder materials, all impacting the way materials degrade and the decisions needed to stabilize and reduce loss of cultural information, and historically, all requiring sampling for accurate characterization and identification. This diverse composite of characteristics greatly complicates the challenges of preserving our cultural heritage.
The Preservation Research and Testing Division (PRTD) at the Library of Congress have created a scientific reference sample collection – the Center for Library Analytical Scientific Samples (CLASS) – with a collection of all the materials found in heritage items. These reference materials have been analyzed with a range of instrumentation and analytical techniques – both non-invasively and through destructive samples – to provide baseline data that can then be correlated with properties found in historic collection items, and with the destructive testing and accelerated aging, can then be used to predict longevity and the impact of various environmental conditions. In addition, often many rare collection items can only be in the research labs for short periods of time, so a go-team of staff has been created to efficiently collect a diverse range of complementary data from the specific collection item in that time. These portable and lab-based instruments include multispectral imaging (reflectance, transmitted and raking) as the baseline mapping of the object, Fourier Transform Infrared spectroscopy (FTIR) – diffuse and reflectance, X-Ray fluorescence spectroscopy (XRF) point and linescan, Fiber Optic Reflectance Spectropscopy (FORS), 3D fluorescence spectroscopy, Raman spectroscopy and other specific techniques that best relate to the material type, and micro-sampling with size exclusion chromatography (SEC) has been correlated to loss of mechanical properties to predict impact of treatments. As a further preservation component, extensive testing of volatile organic compounds (VOCs) with thermal desorption gas chromatography mass spectroscopy (TD-GCMS) to quantify and identify damaging emissions from building and storage materials,
Detecting changes due to exposure of historic documents and objects to various environmental conditions, treatments and the assessment of changes during exhibition of light-sensitive materials is critical for preservation and monitoring deterioration or changes due to these conditions assists in understanding the degradation mechanisms. Multivariate image analysis, chemometrics and data fusion processing techniques have been used to analyze these datasets using Solo+MIA, ImageJ, Matlab and ENVI software. Examples of linked spectroscopic datasets will be discussed for a range of historic documents including 15th century Block books, founding father documents, unique historic comic book hero’s, 21st century political cartoons, pre-Columbian ceramics, textiles, historic pigments and sound recordings.
|
