How did artists create and use color two thousand years ago? Much of the information we have comes from ancient historians, who made observations about the natural world, technology, and trade. But new discoveries are also being made through scientific investigation. Sometimes color on an ancient object is clearly visible — like with the colorful Fayum portrait — but in other cases only microscopic traces remain.
In Investigating Color you will learn about some of the tools scientists and conservators use to answer questions about how ancient artists painted, dyed, and decorated works of art. Scientific instruments used in chemistry, biology, materials science, and other fields have been adapted to locate traces of color, identify unknown color on artifacts, and help us learn more about artists’ materials. As more artifacts are studied, we understand more about how Romans created and used color.
A photographic technique in which the painted surface of an artifact is illuminated with ultraviolet, visible, and infrared light sources. The paint’s distinct reflectance, absorption, and emission of each specific source of radiation is captured in a photo, and can be used to determine what materials are present in the paint surface.
Read a blog post featuring former Kelsey conservation intern Amaris Sturm.
Like multispectral imaging, hyperspectral imaging works by illuminating a painted surface with a range of radiation sources across the electromagnetic spectrum. It does so in greater detail, recording information at many more wavelengths and generating more images and material data from a paint surface.
A 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.
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.
FTIR: 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.
Raman: as above, with two differences. It uses visible and infrared radiation sources, and measures a phenomenon called “Raman scattering” in a paint sample. View American Chemical Society’s webpage on C.V. Raman, the Indian physicist who first discovered Raman scattering.
A crushed paint sample is viewed under a microscope through transmitted, polarized light. Individual pigment particles can be visually identified by manipulating the direction of the light as it moves through them.
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!)
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.
Provides information on trace amounts of metal and isotopes present in a paint sample. This technique was used to measure the isotopic ratios of lead in red lead samples found on the J. Paul Getty Museum’s red shroud mummy, which allowed Getty Conservation Institute scientists to conclude that the red lead pigment used on the mummy came from Rio Tinto, Spain. Read more about this study.