Dressing protective clothing: stabilizing alizarin/halloysite hybrid pigment and beyond

Abstract

Abstract The fading of organic dyes is a serious challenge for conservation of art works. Inspired by the ancient Maya blue pigment, a hybrid pigment of halloysite (Hal) and alizarin (AZ) was prepared by adsorption in aqueous solution. In addition, a layer of polyorganosilane (POS) is used to cover the surface of the hybrid pigment to enhance the chemical resistance and photostability. The hybrid pigments were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and thermal analysis. The adsorption behavior of AZ onto Hal was investigated and optimized. AZ-Hal hybrid pigment was prepared at pH\u202f=\u202f9. Chemical stability was checked by 1\u202fmol/L HCl, 1\u202fmol/L NaOH and ethanol attack. Photostability was evaluated by exposing the pigment to visible light for 360\u202fh, which is equal to more than 28 years in a common museum. AZ molecules were adsorbed on the external and/or internal surface via physical adsorption and hydrogen bonds. The presence of POS in the hybrid pigment influences positively the chemical and light resistance. This may be due to the protective layer that isolates sensitive dyes and oxidising agents.