In-situ study of the consolidation of wall paintings using commercial and newly developed consolidants

This paper presents a comparison of consolidant effectiveness for a newly developed consolidant based on soluble calcium compound calcium acetoacetate and two nano-lime-based consolidants available on the market, i.e., CaLoSiL® E15 and Nanorestore®. Impressionist wall paintings made using the fresco technique in the Franciscan Church in Ljubljana were selected for in-situ studies. In order to monitor the colour differences and consolidation effectiveness before, and a few months after, the application of the consolidants, different non-destructive and micro-destructive methods were used. The colour differences were assessed visually and using spectrophotometry, while the consolidation effectiveness was monitored using three methods: the ultrasound velocity method, the surface hardness method and the DRMS method. We demonstrated the best recovery in terms of mechanical properties and with a negligible effect on the wall paintings' appearances after the treatment with the new consolidant. Both nano-lime-based consolidants show a less pronounced reinforcement in the mechanical strength - smaller increase in the drilling-resistance and the surface hardness. The formation of a white haze with the nano-lime consolidants led to a considerable change in the colours of the wall paintings.