Abstract
Sixteen glazes on medieval (14th–16th century AD) pottery fragments from
Vega pottery workshop (Burgos, Spain) were characterized to investigate the
production technology. To this end, Raman spectroscopy and scanning
electron microscopy coupled with energy dispersive X-ray spectroscopy
(SEM-EDX) were used. The studied glaze samples correspond to fragments of
high-quality glazed ware used by the wealthiest society in the city of Burgos.
The most representative types of glazes, corresponding to honey-marble,
honey-yellow, bright light green, and dark green types, were analysed. Raman
spectroscopy shows lead was used as a fluxing agent in glaze production. SEMEDX
analysis confirms the use of lead oxide and evidences that most of the
samples underwent at least two firing processes. No Raman signals of crystalline
phases were detected on either glaze surfaces or glaze thin-sections. The
exception is the single firing of dark green glazes, which show pseudobrookite
and rutile at the clay body/glaze interface measured in thin section. No colouring
crystalline phases were identified by Raman spectroscopy either. However,
SEM-EDX shows iron was the most-used colouring agent whereas copper
was used for bright light green glazes. The polymerization index (Ip) values
were used to estimate the firing temperatures. The polymerization index values
are typically low for lead glazes and indicate firing temperatures below 700 C.