Low Molecular Weight Cellulose Ethers as Aerosols for the Consolidation of Cohesively Weak Paint Layers

Due to Edvard Munch’s (1863-1944) unconventional painting technique, choice of materials, and the unstable climate conditions of his studios, where the paintings were stored during his lifetime, many of his paintings, now housed at MUNCH, have cohesively weak and loose paint layers. As a result, consolidation and re-adhesion of these fragile paint layers are the most frequently performed conservation treatments on his paintings. A selection of low molecular weight (lmw) hydroxypropyl methylcellulose ethers (HPMC), new to the field of conservation, have been evaluated in comparison to methylcellulose (MC) A4C and sturgeon glue regarding their suitability for the consolidation of cohesively weak paint layers. The mock-ups used for these investigations were of a similar composition (pigment, binding medium and pigment-binding medium ratio) and porosity to a paint sample from the painting “Beach Landscape with Trees and Boats” from 1905-06 by Edvard Munch. Viscosity and surface tension of aqueous solutions of the consolidants and their influence on the imbibition time and depth into porous paint layers were investigated. Fluorescence labelling was used to visualize the imbibition depth of an aqueous solution of the lmw HPMC E3 and MC A4C, applied as an aerosol. With this method it could be shown that the applied amount and the application method of the consolidant (with or without intermediate drying steps) can play a crucial role in the imbibition depth. To evaluate the consolidation effect of the tested polymers, the aerosols of their aqueous solutions were applied on the paint mock-ups in a reproducible and standardized way, using an automated two-axis-table. A customised abrasion test was developed to evaluate the comparative increase of the paint layer cohesion after consolidation. These preliminary investigations show lmw HPMC as promising alternatives to established consolidants. They allow for an ultrasonic nebulisation in higher concentrations and thus for the paint layer’s consolidation in a lower number of applications.