In-situ technical study of modern paintings - Part 2: Imaging and spectroscopic analysis of zinc white in paintings from 1889 to 1940 by Alessandro Milesi (1856-1945).
We present a multi-analytical in situ non-invasive study of a series of emblematic paintings by Alessandro Milesi (1856-1945) from the collection of the International Gallery of Modern Art Ca' Pesaro in Venice. Eight paintings dated from 1897 to 1910 were studied with imaging and spectroscopic techniques. White pigments were characterized by a combination of X-ray fluorescence spectroscopy which traced the presence of zinc-based pigments in Milesi's paintings, Raman Spectroscopy, Laser Induced Fluorescence (LIF) Spectroscopy and Time-resolved Luminescence Imaging. Time-resolved analysis of luminescence emissions revealed the nanosecond emission from organic compounds and the slower emission from the luminescent inorganic pigment Zinc Oxide that varied between 1.1 and 1.6 microseconds. In this work, data regarding the distribution of luminescent pigments was acquired with a time-gated imaging detector. Furthermore, differences in emission decay kinetics recorded from different paintings can be ascribed to different paint formulations or origins of the Zinc white in paint.
On the discovery of an unusual luminescent pigment in Van Gogh’s painting “Les bretonnes et le pardon de pont Aven”
Spectrally and lifetime-resolved UV-induced luminescence imaging have been applied to the in situ analysis of Vincent Van Gogh’s painting on paper “Les bretonnes et le pardon de pont Aven”. The in situ investigation revealed the presence of an unusual microsecond green emission from the white painted areas of the watercolour, and this long-lived emission has not been reported in modern paintings by other authors. In order to attribute and suggest an identification of the luminescent pigment, our analysis was integrated with further measurements on commercially available modern white pigments (zinc white, Lithopone white, Blanc Fixe, zinc sulphide, and copper-doped zinc sulphide) and with an in-depth study of the synthesis processes of zinc-based pigments available at the end of the 19th century. Analysis suggested an attribution of the unusual emission from the Van Gogh painting to a particular variety of zinc sulphide pigment, characterized by the presence of copper impurities which were unintentionally introduced in the crystal matrix during its production. The present study is the first application of lifetime imaging for the mapping of long-lived luminescence from the semi-conductor pigment.
Microbial flora of frozen tail meat from captive Nile crocodiles (Crocodylus niloticus).
Frozen tail meat samples from nine Nile crocodiles (Crocodylus niloticus) were evaluated for microbial numbers and types. Microbial analyses yielded a mean aerobic plate count (APC, 30 degrees C) of 4.86 log cfu/g, a mean coliform count (TC, 37 degrees C) of 3.77 log cfu/g and a mean faecal coliform count (FC, 44 degrees C) of 3.40 log cfu/g. Salmonella was isolated from three samples, and beta-haemolytic streptococci from two samples. Yersinia, Aeromonas, Staphylococcus aureus and Bacillus cereus were not isolated. Typical bacterial genera recovered included Flavobacterium, Pseudomonas, Acinetobacter, Enterobacter, Moraxella, Micrococcus, Staphylococcus and Streptococcus.