Consolidating mural plaster layer with nanolime

 

Treatment of the mural plaster layer with NL. a) Spraying of NL dispersion on the surface of the mural plaster layer. b) Spraying deionized water onto the surface after 10 min the application of the NL dispersion. c) Mural plaster layer, with NL applied for consolidation in samples 1, 2, and 3. d) Mural plaster layer after consolidation. e), f), g) Samples 1, 2, and 3 before consolidation, respectively. h), i), j) Samples 1, 2, and 3 after consolidation, respectively. k) Mural pigment layer of samples 1, 2, and 3.

The pigment of many ancient mural paintings rests on a layer of lime and clay known as plaster, which deteriorates with aging, leading to a decrease in its mechanical strength. A team of researchers from China and Spain studied methods to strengthen the plaster layer using lime nanoparticles or nanolime (NL), a dispersion of calcium hydroxide nanoparticles. NL overcomes the limitations of other consolidants, such as organic materials or acrylic resins, which reduce the breathability of the material and, over time, generate new aging-related problems.

The researchers developed a synthesis procedure to produce NL with uniform size and morphology by using different additives, ultrasonic treatment, and centrifugation. As a result, they obtained nanoparticles of approximately 40 nm in diameter—significantly smaller than the 180 nm obtained without centrifugation. A dispersion of nanolime in ethanol was sprayed with an atomizer onto the plaster layers of fragments from a Chinese mural painting, which were later sprayed with water to accelerate the consolidation of the plaster.

The results showed that the selected nanolime penetrated to a depth of 1.2–3.5 mm, and the surface hardness of the layer increased by approximately 56%. Porosity decreased only minimally (around 5.9%); a slight shift toward smaller pores was observed, indicating effective filling of the structure. Microstructural analysis confirmed the densification of the surface layers after consolidation. No whitening of the pigment layer on the surface of the plaster was observed.

The authors concluded that the nanoparticle-sized selected NL provides high-quality consolidation of mural painting plaster and may serve as a methodological alternative for broader application in the conservation of cultural heritage, including murals detached from their original support and preserved in museums.

For further information go to: JOURNAL OF CULTURAL HERITAGE