During recent restoration works of the Royal Palace in Amsterdam, the marble reliefs in the pediments were surveyed in detail. Mapping of the east pediment revealed that about a quarter of the original white Carrara marble has been replaced by sandstone. Renewing of these fragments presumably dates from the 1930s. The west relief shows the most severe decay, due to the fact that the statues here are facing the rain. SEM research and X-ray micro-analysis of marble crusts showed the ocurrence of salts with a dominance of gypsum (CaSO4.2H2O). The calcium sulphate is formed by the dissolution of calcium in 'acid rain', trapped in the outer pores of the stones. Environmental pollutants, among others fly ash and lead, were also found in the crusts on the marble statues.