To learn more about color use in Roman Egypt, we have focused on three specific technical research questions:
- Is there color on this object?
- What pigments or dyes were used to create that color?
- How often are we seeing particular pigments or dyes?
To answer these questions, we are using three specific examination, imaging, and analysis techniques: digital microscopy, multispectral imaging (MSI), and X-ray fluorescence spectroscopy (XRF). Below, we have outlined what each technique does and why we chose it for this project.
Digital Microscopy
An examination technique that allows us to explore the surface of an artifact at high magnification for traces of pigment and to look closely at how textile threads are dyed. Can be used with the aid of a monitor and to capture digital images at that magnification.
Multispectral/Multiband Imaging (MSI)
A photographic technique in which the painted surface of an artifact is illuminated with ultraviolet, visible, and infrared light sources. Pigments absorb, reflect, and emit light in characteristic ways that can be captured in an image, so we use this technique to learn what pigments or dyes might be present in a painted area on an object or in a dyed textile.
We commonly use the following types of MSI:
- Visible light (VIS)
- Ultraviolet-induced luminescence (UVL)
- Visible-induced luminescence (VIL)
- Infrared reflected false color (IRRFC)
- Multiband reflectance or Indigo Subtraction (MBR Indigo) to reveal indigo.
Multispectral/Multiband Imaging (MSI)
A photographic technique in which the painted surface of an artifact is illuminated with ultraviolet, visible, and infrared light sources. Pigments absorb, reflect, and emit light in characteristic ways that can be captured in an image, so we use this technique to learn what pigments or dyes might be present in a painted area on an object or in a dyed textile.
We commonly use the following types of MSI:
- Visible light (VIS)
- Ultraviolet-induced luminescence (UVL)
- Visible-induced luminescence (VIL)
- Infrared reflected false color (IRRFC)
- Multiband reflectance or Indigo Subtraction (MBR Indigo) to reveal indigo.
X-Ray Fluorescence Spectroscopy (XRF)
An elemental (or chemical) analysis technique in which the painted surface of the artifact is hit with an X-ray beam. The beam causes electronic transitions within the atoms of the sample, a phenomenon that can be measured and recorded as a spectrum. The spectrum is used to determine which elements are present in the paint surface, which can help us identify an unknown pigment.
Techniques for Further Analysis
Fiber Optic Reflectance Spectroscopy (FORS)
A technique in which different wavelengths of light are directed onto the painted surface of an artifact using an optical fiber bundle. The FORS instrument measures the degrees to which radiation is absorbed and reflected by the painted surface, which can reveal what pigments or dyes are present in the paint.
Fourier Transform Infrared Spectroscopy (FTIR)
In this technique, a paint sample (or artifact surface) is hit with a beam of infrared radiation. The molecules in the sample will absorb specific wavelengths of this radiation, causing them to vibrate. The characteristic absorption of the radiation can be measured and displayed as a spectrum that reveals what materials are present in the sample.
Near Infrared Spectroscopy (NIRS)
Similar to FTIR, NIRS uses infrared radiation closer to the visible range.
Raman Spectroscopy (Raman)
In Raman, a sample is hit with a beam of monochromatic light, often from a laser. The light interacts with the molecular bonds in the sample, producing a short-lived shift in energy and re-emission of the light. Known as Raman Scattering, this re-emission of light occurs in patterns unique to different substances. Raman can be used to identify binding media, pigments, and dyes.
Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS)
As with XRF, SEM-EDS microanalysis uses X-rays to identify elements in a paint sample. SEM-EDS works on a much smaller scale, capturing images and identifying materials of a sample at the micron level—small enough to see the scales on a human hair!
X-Ray Diffraction (XRD)
An analytical technique used for the identification of crystalline materials, including mineral pigments. Generates an X-ray diffraction pattern that is unique to each crystal structure.
Liquid Chromatography Coupled with Mass Spectroscopy (LCMS)
Liquid chromatography is a technique that separates the sample (like a dye) while dissolved in a liquid phase into its various chemical components. Mass spectroscopy measures the ratio of mass-to-charge of ions and can be used to determine the elements and isotopes present in the separated components of a sample.