The present study focuses on applying a compatible protective treatment for historical pictorial surfaces in ‘El-Harem palace' (the National Military Museum of Egypt). For this purpose, laboratory painted samples were prepared according to the original materials. The models were treated with acrylic-based polymeric materials, including Paraloid B72, Lascaux® Hydroground 750, and Pébéo Satin Matt Picture Varnish (a transparent varnish of an acrylic resin and polyethylene wax). The stability of the treated surfaces against accelerated UV and thermal ageing was evaluated via optical microscopy (OM), colour measurements, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). The results showed that the behaviour of the tested polymers against accelerated ageing tests is comparable, to some extent. Based on its acceptable stability, Pébéo Satin Matt picture varnish was used as a protective coating for the murals. Significantly, the results of this research will help in protecting rare examples of Rococo-style mural paintings in Egypt.