Cleaning materials: A compositional multi-analytical characterization of commercial agar powders

Effectiveness and selectivity are the main requirements for a proper cleaning of artworks. The complexity of the soiling and the limits of traditional cleaning methods make it necessary to increase the knowledge on the chemical and physical mechanisms involved in cleaning methods. Agar gels have been successfully used in the restoration practise, but it is not yet clarified if their cleaning capability is due only to the solvent action or also to the polysaccharide structure. A multi-analytical procedure including elemental analyses, vibrational spectroscopies, thermogravimetric analysis and pyrolysis-gas chromatography/mass spectrometry is proposed to characterize agar powders in terms of morphology, composition and thermal stability, and to differentiate agar products intended for different applications, i.e. conservation of Cultural Heritage, biology and food industry. The multi-analytical approach proposed allows differentiating agar samples with slight compositional differences. In particular, agar products can be rapidly differentiated by a semi-quantitative analysis of pyrolysis-gas chromatography/mass spectrometry data. The results presented show that agar powders used for cleaning treatments contain impurities probably derived from cellulosic residues.