Colour Stability of Natural Adhesives – Light Ageing of Adhesive Films and Colour Changes of Pigment Layers after Aerosol Application

Abstract

Two aspects of consolidation of powdery paint layers are discussed in this paper: First, the colour stability of different consolidation media including cellulose and protein based materials was evaluated. Film sheet samples of the adhesives were exposed to a Xenontester for 276 hours to reach Blue Wool Standard 7. Light exposure caused loss of colour rather than yellowing in most adhesives which correlates to microfading tests. Secondly, colour changes of the pigment layer during application of consolidation media with an aerosol generator were examined. Any shift of colour results in a change of surface structure rather than a detectable shift seen in the ΔE* ab -values and the reflectance graphs. Thus, the application of aerosols is a very controllable, long-term stable method and results only in minor changes when applied in multiple layers.

Innovation in Green Materials for the Non-Contact Stabilization of Sensitive Works of Art: Preliminary Assessment and the First Application of Ultra-Low Viscosity Hydroxypropyl Methylcellulose (HPMC) by Ultrasonic Misting to Consolidate Unstable Porous and Powdery Media

“…Arguably, the dramatic darkening of Funori may be explained by the Maillard "cooking" reactions, which take place between the carbohydrates and proteins at elevated temperatures (similar "cooking" reactions make butter croissants brown). Funori is a polysaccharide, but contains around 12% and Jun-Funori 1.3% of proteins [38], which may play an important role in discoloration. Typically, the Maillard reactions require around 120 • C dry, however in this testing, 80 • C combined with an extended period of time and an elevated humidity (90 days, 80 • C, 65% RH) might have sufficed for the Maillard reactions to take place [39][40][41].…”