Cellulose nanocrystal stabilized beeswax dispersions for consolidation of encaustic paintings.

We present formulations of dispersions based on beeswax for consolidating encaustic paintings, which use beeswax as a binder and are applied on a canvas or wooden substrate. Commercial natural and synthetic adhesives are used for consolidation of such paintings, but they often have problems due to the consolidant material not being compatible with the original painting. The dispersions were prepared by combining Pickering beeswax emulsions stabilized by cellulose nanocrystals (CNC) with hydrophobically modified ethylhydroxyethylcellulose (EHM). The drop size of the emulsion varied with the beeswax content and the emulsion drops displayed inclusions of water droplets. These inclusions led upon drying to films that showed a hollow micromorphology, which enhanced the water evaporation, giving high breathability. The dispersions comprising beeswax, CNC and EHM were stable over time and the viscosity was governed by the amount of EHM in the formulation. The dried films were very hydrophobic with a water contact angle of about 130°. The emulsion-based formulations were tested on encaustic painting mock-ups made on wood substrate to examine their adhesive strength and water resistance. The formulations achieved better performance than commercial products used as consolidants for encaustic paintings. The beeswax-based compositions, which contain only green components and free of volatile organic compounds, offer an interesting platform for consolidation in the field of cultural heritage.