20 September 2005: Chemists uncover renaissance secrets at the V&A

Italian researchers have used x-ray fluorescence and fibre optic spectroscopy to uncover the techniques used by renaissance ceramics artist Maestro Giorgio Andreoli.

Ceramicists like Andreoli, who worked in Italy in the 16th century, applied concoctions of copper and silver salts, oxides and other substances in a reductive atmosphere to achieve the lustre finishes for which they are remembered.

Constanza Miliani from the University of Perugia, working in an EU-funded mobile laboratory called Molab, assisted Lucia Burgio, an object analysis scientist at the Victoria and Albert Museum (V&A), London, UK, in investigating eight of Andreoli’s lustreware pieces. 

Raman spectroscopy, a light reflective technique that can give valuable information on molecular structure and environment, showed lower than expected Raman scattering in Andreoli’s glaze. 

Miliani suggests this could be the result of silver and copper penetrating the glaze, which softens as it is refired for a third time at the relatively low temperature of 500-600?C to give the lustre finish. The silica network of the glaze is modified as ions are exchanged during the lustre formation process. Miliani predicts that once they have penetrated the glaze, the metals form shimmering nanoparticles.

Andreoli’s pieces also included cassiterite (SnO₂), which he used both as an opacifier and as a white pigment. Lead-antimonate yellow (Pb₂Sb₂0₇) known as Naples yellow was detected on the ceramics, along with an unusual orange decoration containing a high amount of zinc along with lead and antimony, which gave a Raman spectrum slightly different to that of the Naples yellow. 

’These findings strongly suggest the use of an unusual pigment called giallo dei vasari (pottery makers’ yellow), reported in renaissance recipes as a mixture of lead-antimonate yellow and zinc oxide,’ said Miliani.

Ancient texts on glazing techniques are used as reference materials by curators and conservators to understand how the pieces were made. But when modern investigators try the recipes outlined in these tracts they do not always have the desired results. Some art historians speculate that past masters did not always give the full details, or were even deliberately misleading in order to guard their trade secrets from contemporary competitors. 

Burgio’s report of the work will appear soon in the V&A’s Conservation Journal. Helen Carmichael