Methods

In 2021, the polychromy research team was allocated a brand-new, fifty square meters laboratory with new equipment, located adjacent to the museum galleries of ancient art.

Objects are first investigated by multispectral imaging that allows us to characterize materials, including pigments. Typically, the imaging techniques employed are visible light photography (VIS), raking light photography, infrared (IR) photography, ultraviolet-induced visible fluorescence (UVF) imaging, and visible light induced infrared luminescence (VIL) imaging. A technique often called multi band reflectance (MBR) imaging is used when applicable.

IR photography characterizes materials in the near infrared spectral range and complements the documentation with normal light (VIS) illumination. UVF imaging detects materials that fluoresce under UV illumination such as many organic pigments e.g. madder lake. VIL imaging is an effective way of identifying even small remains of the ancient, synthetic pigment Egyptian blue based on the ability of the pigment to absorb visible light and luminesce in the near‐infrared region. MBR imaging can help detect indigo but is sensitive to other materials as well. AIC imaging guidelines ¹ as well as best practice recommendations by the British Museum ² are used.

Additional analytical tools available are cross-sectional analysis of e.g. layered paint samples and microscopy of microsamples. Furthermore, elemental composition of the surface of the objects can be analysed with handheld X-ray fluorescence spectroscopy (hXRF). Fourier Transform Infrared (FTIR) and Raman spectroscopy is conducted at the Center for Advanced Bioimaging (CAB) at the University of Copenhagen.

Depending on the research question, additional methods are applied through collaborations with other research institutions in Denmark and abroad. These methods include but are not limited to: Scanning Electron Microscopy/Energy-Dispersive X-Ray spectroscopy (SEM/EDX) and X-Ray Diffraction (XRD); Liquid Chromatography-Mass Spectrometry (LC-MS) for proteomics, and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for isotopic analysis.

¹ Warda, Jeffrey, Franziska Frey, Dawn Heller, Dan Kushel, Timothy Vitale, and Gawain Weaver. 2017. The AIC Guide to Digital Photography and Conservation Documentation, edited by J. Warda, 3rd ed. American Institute for Conservation.
² Dyer, J., Verri, G., Cupitt, J., 2013. Multispectral Imaging in Reflectance and Photo-induced Luminescence modes: A User Manual. The British Museum.