Lynn Chua

Fifty-five batik textiles produced along coastal Java in the late 19th to early 20th century were analysed to study the red dyes and the cotton fabrics. Surface-Enhanced Raman Spectroscopy (SERS) classified the dyes into six groups and identified 70% of the samples as Morinda. High-Performance Liquid Chromatography coupled with a diode array detector and tandem Mass Spectrometry (HPLC-DAD-MS/MS) confirmed the SERS results and identified synthetic dyes in the remaining samples, which were used either alone or in mixtures with Morinda or indigo. Synthetic alizarin (C.I. 58000, Mordant Red 11) was the most frequently detected synthetic dye. Auramine O (C.I. 41000, Basic Yellow 2), fuchsin (C.I. 42510, Basic Violet 14), and rhodamine B (C.I. 45170, Basic Violet 10) were occasionally detected. The results also highlighted two possible types of Morinda and two variations of synthetic alizarin. The shades obtained from mixtures of natural and synthetic dyes were visually indistinguishable from those obtained with pure natural or synthetic dye, as confirmed by colourimetry. The variety of dyes and cotton fabrics shared across batik producers makes it challenging to attribute unsigned batiks to specific workshops. Nevertheless, this study demonstrated that synthetic dye uptake during this period was limited and experimental, with natural Morinda remaining the preferred choice despite the availability of European synthetic alternatives.

ATR–FTIR (attenuated total reflection–Fourier-transform infrared) microscopy with imaging is widely used in the heritage field to characterise complex compositions of paint cross-sections. However, some limitations include the need for ATR crystal contact with the sample and the inability to resolve particle size below the IR diffraction limit. Recently, a novel O-PTIR (optical-photothermal infrared) spectroscopy technique claimed to open a new avenue for non-invasive, efficient, and reliable analysis at sub-micron resolution. O-PTIR produces transmission-like FTIR spectra for interpretation, without the need to touch the sample, which are highly favourable attributes for analysing heritage samples. This paper reports the comparison of O-PTIR and ATR–FTIR techniques applied to a cross-section embedding a thin paint fragment that delaminated from a late 19th to early 20th-century oil portrait. The hazy paint fragment consisted of zinc soaps (both crystalline and amorphous), gordaite (NaZn₄Cl(OH)₆SO₄·6H₂O), and zinc lactate, that could not all be well-resolved with ATR–FTIR imaging. With O-PTIR analysis, the degradation compounds could be resolved at sub-micron resolution with an equivalent or better signal-to-noise ratio. This case study shows how the two techniques can be used to obtain comprehensive information at a broad level with ATR–FTIR and a detailed level with O-PTIR.

Two Burmese oil paintings on zinc supports depicting portraits of royal families, dated to the early 20th century by Saya Aye and Saya Mya, showed interesting corrosion, efflorescence and soapy globules for analytical investigation prior to conservation for exhibition. The features and colours on the two paintings, one of which was in worse condition than the other, were obscured by a whitish haze. Paint rupture and losses due to corrosion of the zinc support were apparent. Using a combination of 3D digital microscopy, FTIR microscopy and SEM–EDS, the degradation, as well as the paint materials and artists’ techniques were analysed and discussed. Zinc soaps, oxalates, silicates, hydroxychlorides, carbonates, wax and mould characterized the haze. Interestingly, brown outlines in Aye’s painting appeared unusually dark. Upon analysis, this degradation phenomenon was attributed to micro-sized greenish soap globules that have developed around copper/zinc (brass) particles, causing the brown outlines to lose their intended luminosity. The other painting by Mya, in which the same brown outline was applied, did not show such formation of globules. Detection of oxalates in the corrosion of zinc support and brown outlines are discussed. This study shows the importance in understanding the artists’ materials and techniques, which have consequential effects to the degradation observed.

Four brightly colored calligraphic prints from the “Poem” series (1970/71) by Japanese artist Haku Maki (1924–2000) were examined using multiple light-based analytical techniques in an effort to address conservation concerns regarding these artworks. A distracting white haze on the surface of some of the prints was determined by light microscopy and infrared microanalysis to be fungal mycelium from an inactive mold infestation that occurred prior to the artwork’s acquisition by the museum. Pigment analysis by Raman, X-ray fluorescence, and infrared microspectroscopies identified the artist’s palette as containing common printing ink colors such as aniline black (PBk1), carbon black (PBk7), phthalocyanine blue (PB15), Prussian blue (PB27), ultramarine blue (PB29), molybdate orange (PR104), chrome yellow (PY34), barium yellow (PY31), viridian (PG17), barium sulphate (PW21), and synthetic organic red pigments (PR3, PR22, PR48:3). Although aniline black and molybdate orange are common industrial pigments, reference vibrational spectra to assist in their identification have not appeared previously in the conservation literature. Moreover, this investigation includes to the authors’ knowledge the first published identification of these pigments in a work of fine art. Haku Maki’s unique ‘cement-on-woodblock’ printing technique in combination with his vibrant palette creates dynamic, embossed effects in these prints. However, lightfastness testing using a microfade tester identified the potential for light-based damage to the artwork, in some instances showing poorer lightfastness for colors reported to be stable pigments and greater stability than anticipated for others. These analyses are the first objective study of this innovative artist’s material choices, and they enhance our understanding of his printing technique while helping to determine the proper stewardship protocols to protect his artistic legacy.