Earlier this year, we shared a sneak peek of the focus show currently on view in Luce Visible Storage, which highlights William Trost Richards’s watercolor practice. Before the show opened, I examined Richards’s boxes of 19th-century watercolor cakes a bit more closely. This was partly to document the condition and the organization of the watercolors within each box, which could provide clues about the artist’s working practice.

The second goal of examination involved determining whether handwritten labels on some of the individual cakes are accurate. The first label in question was written in ink on the bottom of a ceramic pan holding a medium green watercolor cake: “Emerald Green.” This caught my eye immediately, because this copper acetoarsenite green is extremely poisonous. X-ray fluorescence spectroscopy (XRF) confirmed that, indeed, the watercolor cake is full of arsenic! Plus, although the watercolor is bound in gum arabic, the long, active history of these items during use by the artist and after means that some arsenic-contaminated dust is loose within the box. All storage materials and documentation related to the box of watercolors are now labeled with warnings, and extra precaution is used for handling.

Multiband imaging (MBI) was used to quickly get a sense of whether other labels on watercolor cakes were accurate, and the results were mixed. For example, bright orange or pink luminescence in ultraviolet (UV) illumination indicates a colorant in the red lake family, such as madder or carmine. The variety of oranges and pinks visible in the UV image above means that Richards certainly used a variety of red lakes – but only some of the handwritten labels correspond appropriately.

To completely sort out the watercolor cake colors, much more analysis (and time!) would be required. It would be especially fascinating to analyze the watercolor paintings at the same time, potentially making direct connections between the art supplies and these stunning artworks.

Stop by Luce Visible Storage this spring and summer to view this lovely show.

As we have previously described, we have been experimenting with the use of multiband imaging in the Brooklyn Museum Conservation Lab to help with the mapping and characterization of blue colorants on many pieces in our Infinite Blue exhibition.

We have used infrared subtraction imaging, in combination with other analytical techniques, to characterize indigo on Japanese woodblock prints, and on an ancient Egyptian footcase. Most recently, Victoria Schussler provided a detailed description of this technique for the imaging of a small Fabergé watch-clock with lapis lazuli.

Infrared subtraction imaging can also be used to map the presence of Maya blue. Created by heating a mixture of indigo and the clay mineral palygorskite, this colorant was used by the ancient Maya of Mesoamerica to decorate wall paintings, figurines, ceramics and other ancient ritual objects. In 2008 (Antiquity 2008, 82, 151-164), anthropologists found that Maya blue was produced as part of Maya sacrificial ceremonies, when indigo was fused with palygorskite by burning it along with copal incense. The creation of this extremely durable pigment was a remarkable technical achievement, and the colorant has survived for nearly 2000 years in some cases.

On this Maya figurine and headdress (2009.2.18a-b, 600-900CE), Fourier transform infrared spectroscopy identified the colorant as Maya blue in two small regions. Infrared subtraction imaging helped to further create a map of the indigo-based colorant throughout, which appears as bright white in the infrared subtraction images. You can currently see this remarkable figurine and its removable headdress on display in our Infinite Blue galleries.