Fig. 10

ATR/FTIR of the plates prior to soiling. Except for the beeswax coated plates all other plates show the characteristic gypsum bands (Additional file 1: Table S3) indicating the absorption of the coatings into the gypsum substrate. Linseed oil (CL and BL) and shellac resin coated plates (SR6 and SR18) have a carbonyl signal at 1740 and 1722 cm⁻¹ that appears as a shoulder of the weak band at 1680 cm⁻¹ due to O-H bending of gypsum, and the barite-Ca(OH)₂ (BC) has characteristic peals of calcite at 1410 cm⁻¹, 1066 cm⁻¹, 875 cm⁻¹ and aragonite at 856 cm⁻¹ and 713 cm⁻¹. Beeswax (WX) generated a film over the plaster substrate