Vibrational spectroscopy to study degradation of natural dyes. Assessment of oxygen-free cassette for safe exposition of artefacts

Abstract

An important issue connected with conservation chemistry is how to improve the storage and exposure conditions in order to suppress the fading and degradation of dyes and other components of paintings. Although the oxygen-free exposure cassettes are commonly known in museums, there is still lack of information in the literature about the effect of anoxic conditions on the degradation of dyes. This study is an attempt to start a database formation on the dyes degradation. Five commercial dyes (indigo, dragon's blood, curcumin, madder, carminic acid) were submitted to accelerated ageing by exposure to intensive light in the visible range in both oxygen-free (anoxia) and -rich conditions. Degradation of the samples was investigated by several analytical techniques (attenuated total reflectance infrared spectroscopy, Raman spectroscopy, reflectance UV-Vis spectroscopy, X-ray fluorescence spectroscopy and optical microscopy). The conclusions are based on the estimators (derived from the determination of colour differences from Vis spectra and from the changes in FTIR and Raman vibrational bands intensity). According to them, only indigo, dragon's blood and curcumin show greater stability in anoxic conditions in comparison with oxygen-rich ones while madder, carminic acid undergo greater degradation.

FTIR analysis and quantification of phenols and flavonoids of five commercially available plants extracts used in wound healing

“…, possibly due to OH groups vibrations [20]; at 2096 cm -1 is a non-identified band; at 1632 cm -1 , it could be related to stretching vibration of aromatic C=C; a "shoulder" at 1526 cm -1 was not identified; at 1450 cm -1 could be due to stretching vibration of aromatic C=C; at 1340 cm -1 could be related to rocking vibration of aromatic CH; at 1291 cm -1 was not identified; at 1209 cm -1 would be due to the stretching vibration of (O-CH3); the band at 1149 cm -1 was not identified; the band at 1080 cm -1 could possibly be related to the stretching vibration of (C-O-C) [30]. The band at 1045 cm -1 was not identified.…”

Approaches for Detecting Madder Lake in Multi-Layered Coating Systems of Historical Bowed String Instruments

“…As expected, characteristic signals generally attributed to the lake pigment were identified (Figure 8a): bands for the hydroxyl stretching (νOH) at 3400 cm −1 , carbonyl groups (νC=O, 1645 cm −1 ), aromatic rings (νC=C, 1530 cm −1 ) and aliphatic chains (δC-H 2 , 1425 cm −1 ), as well as the strong peak of sulfates (νS-O, at 1105 cm −1 ) are clearly identifiable [34,35]. As shown in Figure 8a, the aged ML (t = 520 h) shows a strong increase of the band at 1645 cm −1 , probably due to the presence of degradation products such as benzoic acid, phthalic anhydride and dimethyl phthalate [36].…”

Impact of medium and ambient environment on the photodegradation of carmine in solution and paints

“…Changes in the vibrational spectra suggest that anthraquinones undergo aromatic ring opening and that adsorbed water on the sample can enhance the degradation [14]. Examination of the decolorization mechanism of dyeing effluent by a fungus has provided some insight into the degradation process, showing the fungus degrades the carminic acid via a two-step process of glucose cleavage followed by a ring cleavage reactions [17].…”

“…A study of the stability of the dry pigment, monitored using vibrational spectroscopy, indicated enhanced photodegradation under anoxic conditions [14]. In contrast, anoxic conditions were found to stabilize or slow the photo-induced degradation of carmine lake in paint samples [6,7,15].…”