Project Design
Which research techniques should you consider? Use this color investigation questionnaire to plan your research workflow.
Is there color on this item? Where is it located? Start with A.
Objects
Textiles
What pigments are present? Continue to B, then proceed to C.
What dyes are present? Continue to B.
I’m still not sure which pigments or dyes this color is made of. Consider D.
D. Further Analysis
The techniques used in our color survey can be used to answer certain research questions, while for others, further analysis may be needed. For example:
- What binder was used in this paint layer?
- What are each of the components of this pigment or dye mixture?
- What kind of red iron oxide is this?
Is there color on this item? Where is it located? Start with A.
Objects
Textiles
A. Microscopy
A. Multispectral Imaging
What pigments are present? Continue to B, then proceed to C.
What dyes are present? Continue to B.
B. Multispectral Imaging
B. Microscopy
C. X-Ray Fluorescence Spectroscopy
I’m still not sure which pigments or dyes this color is made of. Consider D.
D. Further Analysis
The techniques used in our color survey can be used to answer certain research questions, while for others, further analysis may be needed. For example:
- What binder was used in this paint layer?
- What are each of the components of this pigment or dye mixture?
- What kind of red iron oxide is this?
Microscopy
Allows us to examine artifacts at high levels of 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.
Ideal for when you have very little pigment left on your object (great for sculpture and ceramic figurines). Use this to determine whether imaging and analysis are worth your time.
Multispectral/Multiband Imaging (MSI)
A photographic technique in which the surface of an artifact is illuminated with ultraviolet, visible, and infrared light sources. Pigments and dyes 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.
Can be used for pigment and dye identification, mapping the locations of pigments and dyes (Egyptian blue and indigo) on an artifact surface, and revealing hard-to-see painted inscriptions.
X-Ray Fluorescence Spectroscopy (XRF)
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, which can help us identify an unknown pigment.
XRF can identify the chemical elements present in a number of inorganic pigments used in antiquity, including iron oxides, arsenic-, copper-, lead-, mercury-, dye-, and fiber-containing pigments, and ground layers such as calcite and gypsum. XRF is not useful for characterizing exact mineral species or organic pigments or dyes.
Further Analysis
For questions like these, additional materials analysis is recommended. For binders, infrared spectroscopy (FTIR, NIR) may be useful; for mixtures, SEM-EDS can be used to identify and visualize the various components of a pigment mixture, while LCMS is the go-to technique for dye identification; to ID a pigment at the molecular level, consider using FTIR and Raman—while X-ray diffraction remains a valuable tool for identifying the exact mineral species of a colorant (see Introduction to the Techniques for more information).
Workflows
The workflows presented here are optimized for the equipment and processing techniques used at the Kelsey Museum. While they were developed for the “Investigating Color in Roman Egypt” project and its particular set of research questions, instruments, and users, they can be adapted to other projects.