Pennsylvania German sulfur-inlaid furniture: characterization, reproduction, and ageing phenomena of the inlays

Eighteenth-century Pennsylvania German furniture inlaid with an ivory-coloured material was first mentioned in the art historical literature in 1958. Since that time, there has been substantial confusion about the composition of these inlays, the source of their colour and their method of manufacture. In 1977, a number of these inlays were identified as an unspecified allotrope of sulfur. Eighteen years later, a second type of ivory-coloured eighteenth century furniture inlay that did not contain sulfur was identified, and a method of reproducing the sulfur inlays by pouring molten sulfur into an incised decoration was demonstrated. The reproductions were structurally successful, containing the air bubble inclusions that are observed in the eighteenth-century inlays, but they were the bright yellow colour that is characteristic of α-S₈, the allotrope of sulfur typically observed at ambient temperatures. Five eighteenth-century Pennsylvania German ivory furniture inlays were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy energy-dispersive x-ray microanalysis, energy dispersive x-ray fluorescence, colorimetry and gas chromatography–mass spectrometry to identify their compositions. Four of the eighteenth-century inlays were found to be pure α-S₈. The inlays were further characterized by colorimetry and non-spinning Debye Scherrer XRD to identify the source of the ivory colour observed in the eighteenth century α-S₈. Data from these experiments suggest that the ivory colour is caused by a particle size decrease of the sulfur that may result from repeated climatic cycling. This would occur over the course of 200 years spent in an uncontrolled environment, and artificial ageing experiments will be used to determine if it is due to the low thermal conductivity of sulfur, a property responsible for the macroscopic cracking and spalling of sulfur in natural history collections. The composition of a sulfur inlay repair and an eighteenth-century non-sulfur ivory-coloured inlay are also presented, along with their roles in the common misconceptions about sulfur inlay.