Fibrous plaster is a historic material of great prevalence within theaters and auditoriums within the UK, but until recently it has been almost completely unresearched. With the partial collapse of the Apollo Theatre ceiling in 2013, there is growing interest in the safe conservation of fibrous plaster. This study investigates the architectural paint coatings originally applied to fibrous plaster sampled from five London theatres and auditoriums built between 1856 and 1919.

A rigorous analysis of the individual paint layers was conducted using carefully prepared polished cross-sections. The finishes applied were identified using state-of-the-art characterisation techniques, including digital microscopy, SEM imaging, SEM-EDX mapping, Raman spectroscopy, Fourier transform infrared spectroscopy, and water solubility testing. The investigations demonstrated that for 20th-century theatres, lead white oil paint has been shown to constitute their early finish history, whereas venues built before the turn of the century were originally decorated with other materials, including distemper, gold size, and gilding.

This is the first systematic research on architectural finishes originally used on fibrous plaster. The results provide important physical and chemical information relating to the coatings used, informing on the most appropriate conservation approaches. It provides a foundation upon which further investigation into this under-researched material can be based.