The paper “New evidence for the intentional use of calomel as a white pigment” is co-authored by Mila Crippa, Stefano Legnaioli, Christine Kimbriel and Paola Ricciardi. It is now published in the Journal of Raman Spectroscopy and is available in open access thanks to an NHSF Gold Open Access grant.
The paper discusses the use of in-situ micro-Raman spectroscopy for the identification of calomel – a mercury (I) chloride mineral with formula Hg2Cl2 – as a white pigment in a 15th-century English manuscript and a late 16th-century portrait miniature by renowned limner Isaac Oliver, both belonging to the Fitzwilliam Museum in Cambridge, UK.
Although mercury chloride compounds have been employed for centuries in different fields including medicine, electrochemistry and cosmetics, the deliberate use of calomel as a pigment has been identified only recently within a few 17th-century South American objects. The present research, however, attests the first-ever verified presence of calomel within the original painting palette of two Western European works of art, predating its documented use in South America.
With ever-increasing possibilities to undertake non-invasive analyses of museum objects, it is quite possible that in the near future, calomel will no longer be considered an unusual pigment but rather will take its place as an integral part of the palette used by artists in different times and places.
The research behind this paper has been financially supported by the Cambridge Humanities Research Grants scheme, the Zeno Karl Schindler Foundation and a Short Term Mobility grant from the Italian National Research Council (CNR).
(Left) Full-page image and detail from the so-called “Fitzwilliam Missal” (Cambridge, Fitzwilliam Museum, MS 34, fol. 138r, York, England, ca. 1470) with coloured dots indicating where Raman analysis was performed; (Centre) Raman spectrum obtained from the white areas analysed on both objects (black line) and reference Raman spectrum of commercially available Hg2Cl2 (red line); (Right) full image and detail of the portrait of an Unknown Lady by Isaac Oliver (Cambridge, Fitzwilliam Museum, FM 3868, England, ca. 1596-1600) with coloured dots indicating where Raman analysis was performed. Image from: https://doi.org/10.1002/jrs.5876.
The Cleaning Modern Oil Paints project (CMOP) is a collaborative European research project, funded through the JPI Heritage Plus programme, which runs from June 2015 – May 2018. The project aims to investigate conservation challenges associated with twentieth and twenty-first century oil paintings in order to ensure that modern oil paintings continue to be fit for display for future generations.
Many unvarnished twentieth and twenty-first century oil paintings are exhibiting unusual water sensitivity. Water sensitivity can be defined as the unwanted removal of pigment and/or original material when a discrete cleaning test is carried out using a dampened cotton swab on the surface of a painting. Water sensitivity is not restricted to a particular oil-paint brand, or artist, and affects a broad range of paintings.
Winsor & Newton Artist Oil Colour swatches that were studied as part of the microchemical journal paper. Copyright Tate.
Water sensitivity is problematic for conservators, since many of the well-established methods for removing surface dirt (which naturally gathers over time) involves the skilled application of water based cleaning systems. Since dry-cleaning methods, for example using dry brushes or specialist sponges, are not always particularly effective at removing soiling, water sensitivity can complicate or even prevent effective treatment. This is problematic as accumulated surface dirt can change the appearance of paintings e.g. through altering the saturation, intensity and gloss of paint passages, and can, over the longer term, contribute to other unwanted side-effects relating to ageing and deterioration.
The interdisciplinary CMOP team have been investigating the underlying causes of water sensitivity in modern oil paints. This information has been used to inform the systematic testing and evaluation of selected cleaning systems for use on water sensitive modern oil paintings, with the aim of informing conservators about the risks involved and how to minimise them.
Part of the CMOP research has involved the chemical analysis of a series of naturally aged modern oil paint micro-samples, taken from case study oil paintings and from historic Winsor & Newton (W&N) artists’ oil paint swatches. The W&N paint swatches were originally produced by the manufacturer for quality control testing, and were subsequently donated to Tate by ColArt UK for research purposes.
W&W Artist Oil Colour swatches studied for the paper, shown in tungsten light (left) and UV light (right). Copyright Tate.
We are pleased to announce that the National Heritage Science Forum has kindly sponsored the Gold Open Access publication of a key CMOP research paper, entitled Scientific investigation into the water sensitivity of twentieth century oil paints, now published in the peer-reviewed Microchemical Journal. This describes an in-depth investigation into the chemical characteristics of water sensitive paint passages, and likely causal factors.
The research at Tate is led by Principal Conservation Scientist Dr Bronwyn Ormsby, with Post-doctoral Researcher Judith Lee, and with the support of Tate’s Collection Care Research. More information on the project and details of the key CMOP project dissemination event; Conference on Modern Oil Paints taking place on 23-25 May 2018, are available on Tate’s website.
Detail of a case study oil painting analysed as part of the project. Copyright Tate.
The National Heritage Science Forum provides Gold Open Access grants to help to open up access to heritage science research. This funding is available to employees, students and members of our member organisations – find out more.
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