Jennifer Poulin

In 1906, Charles T. Currelly participated in excavations at Deir el-Bahri, Egypt, recovering votive offerings from the Temple of Hathor (Dynasty XVIII, reign of Hatshepsut, 1479–1458 BCE). These objects became part of the founding collection of the Royal Ontario Museum, where Currelly served as the first director. Among the offerings are several paintings on linen cloth. During examination of one painted textile, a border fringe with cream (suspected undyed), yellow and blue looped threads was sampled and analysed for dyes using gas chromatography–mass spectrometry. The yellow threads were found to contain a tannin-rich dyestuff, likely derived from Rhus spp., a common dye in ancient Egypt. Unexpectedly, the blue threads yielded brominated-indigoid marker compounds, indicating the use of a Murex-derived dye. While purple shellfish dye is rare due to the high cost of its complex production, blue shellfish dye is even more exceptional and has only been identified a handful of times on archaeological textiles. Calculated values of di-brominated to mono-brominated indigoid compounds suggests the dye originated from an indigotin-rich type of Hexaplex trunculus snail, a Mediterranean species. This finding represents a rare example of blue shellfish dye use in ancient Egypt and provides new insights into the dyeing technologies of Dynasty XVIII and the importance of this sky-blue colour in the worship of the goddess Hathor.

Charles T. Currelly, first director of the Royal Ontario Museum, participated in excavations of the tomb of King Nebhepetre, now known as Mentuhotep II, (Dynasty XI) in Deir el-Bahri, Egypt in 1906. He brought to Canada many objects from the excavations, and objects that he purchased while in Egypt; these formed the initial collection of the museum. Among the objects were seven fragments of fine linen cloth with intricate pleat patterns. Recently, the cloths became the subject of a study to learn how they had retained their pleats for 4000 years. Samples were examined and analysed using polarised light microscopy, scanning electron microscopy-electron dispersive X-ray spectrometry, gas chromatography-mass spectrometry, and pyrolysis-gas chromatography-mass spectrometry. Three of the cloths were likely fragments of clothing re-purposed as bandages and were found to be saturated in mummification balms composed of Pinaceae resin, Pistacia resin, and an essential oil characterised by a high abundance of cedrol, possibly originating from a juniper species. All seven of the cloths were found to have traces of polysaccharides from two probable sources: an arabinogalactan gum such as gum arabic or a fruit gum, and a polyglucoside, possibly starch.

From the invention of Perkin’s Mauve in 1856, to publication of the first edition of the Colour Index in 1924, more than 1200 synthetic organic colourants were introduced. Some achieved commercial success, while others were rarely used for reasons such as high cost, low fastness, and toxicity. This turbulent period of innovation was largely driven by demand of the textile industry; however, synthetic colourants were subsequently adopted in many other applications. An understanding of the most common materials and their properties is therefore important to the study of heritage collections and their preservation. The risk of light damage during exhibition of objects is often a concern due to the fugitive nature of many synthetic colourants. To provide a foundation for focused research on synthetic dye identification and lightfastness, work was carried out to identify the most prominent of these colourants used in North America up to the year 1924 when the first edition of the Colour Index was published. Information was compiled and analysed from several sources including multiple editions of the Colour Index, and government documents related to the manufacture and trade of synthetic dyes that provide data from 1914 onwards. Cross-referencing between the information sources provided a summary of parameters for each colourant including the date of introduction, number of manufacturers, lightfastness, and quantity produced or imported in the United States. A document published in 1916 by the US Department of Commerce listed 259 colours with Schultz number imported during the 1913–1914 fiscal year, in quantities above 10,000 lb (4536 kg). Adding domestic products to the list, and removing duplicates, gave 289 individual colours with Schultz number imported and/or produced in the US. In addition, there were some imports of unknown composition: 96 azo, 23 sulphur, and 68 unclassified. Further review of census data from 1917 through the 1920’s suggested that less than one quarter of the dyes listed in the Colour Index were imported or manufactured in significant amounts. The results of this analysis are presented as summary statistics, which are complemented by an open dataset publication to facilitate future research.

This paper describes an investigation into the causes of specific degradation phenomena in three oil paintings from the 1960s by eminent Indigenous Canadian painter Rita Letendre. A comprehensive technical study of the paintings was undertaken using a combination of SEM-EDS, FTIR spectroscopy, Py-GC-MS, Raman spectroscopy, XRD, and polarised light microscopy to determine pigments, fillers, additives, paint medium, and degradation products. Compositional factors, including high abundances of manufacturers’ additives such as aluminum stearate and castor wax, have likely contributed to the formation of oil exudates and fatty acid efflorescence. Cross sections illustrated an inhomogeneous distribution of additives and incomplete mixing of components in some colours. This appears to be due to the migration of components over time and also to Letendre’s technique, which included application of thick paint directly from the tube and the addition of extra medium to some impastos. Cracking, lifting, and protrusions in several areas were caused by the crystallization of zinc soaps below the paint surface. FTIR mapping allowed the spatial distribution of crystalline and ionomeric-type zinc soaps to be determined within a problematic paint layer.

Shortly after a major renovation at the Royal Ontario Museum, it was noticed that the glass panels in many of the new display cases exhibited fogging or hazing on the surface, sometimes in very specific patterns. Cleaning removed the fogging temporarily, but it began to reappear within 12 months. An investigation of fogged glass panels in display cases was undertaken to understand the source of the fogging and to develop an appropriate cleaning method. This included the analysis of residues from glass panels in several galleries, and surface imaging and compositional analysis of glass panels. The fogging residues on the glass panels consist mainly of sodium salts of organic acids and inorganic anions. Sources of the sodium in the residues include air particulate matter and the glass itself. The organic acids and inorganic anions that form salts with the sodium cations likely originate from volatile organic compounds (VOCs) and particulate matter in the air. Examination of the fogging patterns on the glass panels revealed that the sodium salts grow on marks made during cleaning attempts and the manufacturing process. These cleaning and manufacturing marks contain greasy residues that encourage crystal growth. Because of the variation in surface cleanliness, panels with more cleaning and manufacturing residues appear to be heavily fogged while those with less may appear to be unfogged in the museum display cases. A cleaning protocol was tested on two of the glass panels, and was found to remove all traces of grease and fogging residue.

Dyes derived from brazilwood (Caesalpinia spp.) are known to have been used in a diverse range of objects, from Medieval European textiles to North American First Nations objects, while pigments made from brazilwood feature in the palette of a number of painters, including Rembrandt and Van Gogh. For almost two decades, an unknown marker has been used to detect brazilwood colourants in historical objects. Limited sampling opportunities mean that the identification of the chemical structure of this marker has eluded scientists to date. Using a combination of synthesis, UPLC-ESI-MS/MS, HPLC, NMR and GC-MS, the identity of this unknown marker was confirmed as the benzochromenone, urolithin C. Structural identification provides a reliable reference compound for use across a range of analytical techniques employed in the cultural heritage sector and will enable the future development of non-destructive techniques for its identification on high-status objects.

The derivatising agent m-(trifluoromethyl)phenyltrimethylammonium hydroxide (TMTFTH) has been employed for more than a decade at the Canadian Conservation Institute (CCI) to extract natural dyes from historical textiles and other dyed substrates. The alkaline reagent breaks the bonds between the colourants and the mordant ions or functional groups of the substrate, releasing the dye compounds into the extraction solution, and derivatises polar functionalities to produce compounds that are amenable to subsequent analysis by gas chromatography–mass spectrometry (GC–MS). This approach allows for the identification of the colourants, and is also useful in determining the presence of degradation products from the dyes and substrates, non-dye marker compounds, auxiliary compounds added to the dye bath, and substances present on the object through anthropogenic use, conservation treatments, or possible pesticide contamination. This paper discusses compounds formed through the reactions of TMTFTH with flavonoid dyes (dyer’s buckthorn, old fustic, weld, red sandalwood, and brazilwood), quinone dyes (madder, Relbunium, Galium, cochineal, lac, and walnut), indigoid dyes (indigo, Tyrian purple, and indigo carmine), turmeric, marigold, lupin and several lichen species. Results from a selection of historical dyed textiles and other decorative objects analysed at the CCI are provided to illustrate applications of the methodology.