Understanding the formation of efflorescence on beeswax models housed at the Natural History Museum of Florence

Abstract

The Natural History Museum of Florence, and in particular “La Specola”, houses several ceroplastics collections produced in Florence in the XVIII-XIX centuries by Clemente Susini and co-workers. The collections include models of fruits and plants, vertebrate and invertebrate animals, and over 1400 anatomical waxes. All models are mainly constituted by beeswax. Although extremely resistant, the models undergo a wide range of degradation processes. Periodically, a white crystalline efflorescence, commonly called “wax bloom”, appears on the surface of the objects obviously impairing their aesthetical features.Many mechanisms have been hypothesized about the formation of these white exudates, but non univocal conclusions have yet been drawn. Our gas chromatography-mass spectrometry results indicate that wax bloom strongly depends on the composition of the models, being related to the presence of oils and fats originally used as plasticizers or pigments’ media. Thermal and X-ray measurements indicate that a poor solid-solid miscibility between the efflorescence compounds and other beeswax components leads to phase separation followed by migration of the immiscible materials towards the model surface. Besides, X-ray diffraction reveals an increased structural order of models as compared to recent beeswax certainly correlated with the increased brittleness determined by rheology measurements.