Art experts at the National Gallery of Art in Washington, DC, have long questioned whether two paintings credited to Johannes Vermeer were indeed true works of the venerated artist, or if they may be fakes. While “Girl with the Red Hat” and “Girl with a Flute” are not obviously forged, they have some differences that set them apart from Vermeer’s usual works: they are smaller, painted on wooden panels instead of his usual canvas, and “Girl with a Flute” does not match Vermeer’s usual standards.
The COVID-19 pandemic, which forced museums to close their doors to the public for many months, offered experts the perfect opportunity to take these paintings off display and study them without disappointing the Gallery’s usual stream of visitors. But how can art experts – in this case, imaging scientists – find out more about the works of art without doing any damage?
The answer is in a technology called reflectance imaging spectroscopy, a process that centers on hyperspectral camera systems scanning paintings to gather detailed reflectance information across a range of wavelengths. Different molecules absorb light at different wavelengths, so analysis of wavelengths bouncing off the painting can give scientists valuable insight into what materials may be on each part of the canvas – such as crushed minerals or pulverized insects that were used for paint pigments. The results reveal what was painted in layers underneath the surface, and the artist’s process and phases in developing the works.
Analysis of paintings using this system relies on many years of technological developments and the standards that support them. ANSI/OEOSC OP1.007-2020, For Optics and Electro-Optical Instruments – Optical Elements and Assemblies – Infrared Spectral Bands, is one such standard. Developed by the Optics and Electro-Optics Standards Council (OEOSC), a member and accredited standards developer of the American National Standards Institute (ANSI), this American National Standard provides named subregions, or bands, of the infrared region of the electromagnetic spectrum from 0.750 microns to 30.0 microns. It also defines standard reference wavelengths for the general metrology of infrared materials and components in each of the spectral bands.
Two international standards of the International Organization for Standardization (ISO) provide guidance specific to spectroscopy. ISO 18115-1:2013, Surface Chemical Analysis – Vocabulary, provides general terms for surface chemical analysis, as well as terms specific to spectroscopy. This standard was developed by ISO Technical Committee (TC) 201, Surface Chemical Analysis, Subcommittee (SC) 1, Vocabulary. ASTM International is the ANSI-accredited U.S. Technical Advisory Group (TAG) Administrator to TC 201 and SC 1, and the U.S. holds the secretariat to SC 1.
ISO 18381:2013, Space Data and Information Transfer Systems – Lossless Multispectral and Hyperspectral Image Compression, supports compression of the gigabytes of data produced in the hour-long painting scan. This standard was developed by ISO TC 20, Aircraft and space vehicles, SC 13, Space data and information transfer systems. The U.S. holds the secretariat to this TC and SC, with SAE International acting as U.S. TAG administrator for TC 20 and ASRC Federal as U.S. TAG Administrator for SC 13.
The technology behind reflectance imaging spectroscopy used on paintings is helpful in many other applications as well, utilizing reflected wavelengths to determine what and where certain materials are when they can’t be seen by the naked eye. American National Standards guide these other uses, as well, including:
The jury is still out on whether “Girl with the Red Hat” and “Girl with a Flute” are true Vermeers. Even with the new information provided by the reflectance imaging spectroscopy scans, researchers haven’t reached a conclusion, and there are disagreements among the experts. They are aiming to put their findings into a paper by next year.
Learn more about the Vermeer works in question, and the technologies used to analyze these and other paintings, in The New York Times article: “Peering Under Vermeers Without Peeling Off the Paint.”