Investigation of coloured lead glass glitter from an early eighteenth century material collection, Cambridge, by electron microscopy/energy dispersive X-ray analysis

Abstract

Background: Coloured glass glitter is made from thin glass flakes and used for decoration purposes. Published analytical data mainly originates from restoration sites in different countries and is still fragmentary. Samples are often contaminated or corroded, which makes it difficult to evaluate the results, particularly when these were obtained by near-surface techniques.Context and purpose of the study: For this investigation, six types of coloured glass glitter from an eighteenth century material collection from Cambridge, England were investigated by optical microscopy and electron microscopy/ energy dispersive X-ray analysis in order to obtain a wide range of data, which can be used to examine the production techniques of eighteenth century coloured lead glass glitter. They have been stored in a wooden cabinet for 300 years and were sampled directly from the original small paper boxes. Each sample contained glass flakes of different sizes and thicknesses and even different colours. Results and main findings:All flakes were made of lead glass with lead contents in the range between 18 to over 70 wt%. One group showed mixed alkali compositions, probably from potash, lime and nitre, the other contained sodium, potassium and calcium oxides only in trace, if at all. Colouring elements were cobalt, copper, iron, manganese and gold resulting in blue, green, yellow and violet. Conclusions:Although the colouring elements resemble mostly contemporary recipes as known from Neri and his translators, the glass composition is clearly different and differs also from other lead glass compositions from that time. This is a first indication of the production technology of eighteenth century glass glitter. Brief summary:A wide range of analytical data obtained from early eighteenth century glass flakes is presented here and is discussed with regard to the composition of lead glasses, colouring elements, and manufacture details. Potential implications: Lead containing glass glitter is often found in restoration sites, but their manufacture is still waiting to be thoroughly investigated. Almost nothing is known about its historical manufacture. The study provides a wide range of data, which allow to further increase our knowledge on composition and manufacture of these often used decoration materials from the eighteenth century.

The Reliquary Bust of Saint Lambert from the Liège Cathedral, Belgium: Gemstones and Glass Beads Analysis by pXRF and Raman Spectroscopy

“…, Verità ). The green tint induced by Fe 2 O 3 was certainly eliminated by adding MnO and As 2 O 3 (Steigenberger and Herm ).…”

“…Copper oxide (generally 2 to >10 wt.% CuO) was commonly used to give the blue colour to turquoise glass in the Middle Ages (Biron et al 1996, Cannella 2006, and tin dioxide was added as opacifier agent (Henderson 2000, Mirti 2002, Tite et al 2008, Greiff 2008, Arletti et al 2011, Thornton et al 2014, Verità 2014. The green tint induced by Fe 2 O 3 was certainly eliminated by adding MnO and As 2 O 3 (Steigenberger and Herm 2016).…”

At the Core of the Workshop: Novel Aspects of the Use of Blue Smalt in Two Paintings by Cristóbal de Villalpando

“…conclude that the painters used local cullet as an additive to oil paint. In contrast to the smalt used by Villalpando in the two paintings in this study, the lead-rich glass found reported byLutzenberger et al (2010) had a very high calcium content.18 The "fritta di cristallo" was obtained calcinating a stone rich in quartz, which Neri describes as "Tarso," with ashes from Levante ("polverino").While Neri describes with detail the making of lead glass, he also references the blue smalt that painters used as an independent material; thus, it is hard to affirm whether or not lead glass was used to paint.19 British lead glass (flint glass) has high contents of lead (between 12 and 40 wt.% PbO)(Steigenberger and Herm 2016;Kurkjian and Prindle 1988;Hellemans et al 2014) in comparison with the content found in Villalpando's paintings.…”