Beyond Vitruvius: New Insight in the Technology of Egyptian Blue and Green Frits

Abstract

Archeological campaigns along the track of the Domitian road in Cuma resulted in the recovery of a large amount of potshards and crucible fragments (both open and closed forms), covered with residues of blue and green frits, respectively. Typological analysis of the crucibles combined with mineralogical and petrological analyses on the ceramic body and frit residues revealed that the forms are intimately related to the technological data. Newly formed calcium silicates indicate high firing treatments of crucibles during pigment making (not lower than 950°C). In particular, different working temperatures for the two types of crucibles have been estimated by the presence/absence of sodalite‐nosean feldspathoid. This mineral formed after the reaction of Si‐Al‐rich material (the sintered ceramic body) and alkalis transferred to ceramics via chemical diffusion during the pigment synthesis. Thus, the estimated working temperatures are higher for closed forms (>1100°C) and lower for the open ones (950–1050°C). This different thermal treatment perfectly fits with the temperatures of green and blue pigment synthesis; higher temperatures for green pigments allowed the formation of abundant Cu‐bearing glassy phase, whereas, blue pigment is prone to the formation and thermal stability of cuprorivaite crystals (950–1050°C). Moreover, the two frits showed similar recipes (quartz‐feldspar‐calcite‐rich sand) with the exception of more abundant Cu‐bearing colorant agent in blue hue and higher proportion of alkaline flux in green frit. The obtained data suggested that crucibles were a fundamental tool for pigment manufacturing, likely one of the best example of ancient technical ceramics, as they permitted controlling the temperatures along with the fuel and the treatment time. Combining analytical and archeological data, the production and the technology of the two colored compounds identified as Egyptian Blue and Green frits in ancient Cuma has been inferred. Finally, considering the Vitruvius excerpt that identified an Egyptian Blue production in Puteoli, the area of production can be widen up to the northern Phlegraean Fields, also including Cumae and Liternum.

Local production and imitations of Late Roman pottery from a well in the Roman necropolis of Cuma in Naples, Italy

“…Taking into consideration the textural features (sorting and circularity) and the mineralogical assemblage, such a mixed‐source temper resembled the shoreline deposits from Mondragone to north of Cuma, where beach sands are affected by the flux of siliciclastic and carbonate sediments of the Volturno River with a volcanic component derived from Campanian volcanoes (Balassone et al, ; Morra et al, ). It is worth highlighting that such sand was a valuable geomaterial, largely used in antiquity by Phlegraean artisans (including Cuma) as starting materials for glass and green/blue pigments, as also claimed by Vitruvius (Grifa et al, ). Hence, the cooking pots of presumed Aegean‐like tradition can be considered as imitations since the artifacts from the Eastern Mediterranean pottery tradition are sensibly different as characterized by the occurrence of metamorphic or acidic volcanic‐tempered pastes (Istenič & Schneider, ); moreover, they also differ from other Italian imitations, in which a calcareous paste plus volcanic temper was recognized (Gliozzo et al, ).…”

Egyptian blue pigment in East Mediterranean wall paintings: A study of the lifetime of its optical infrared emission

“…The ancient production of Egyptian blue must have been in the hands of very competent specialists and large workshops for its production has been identified in Amarna and elsewhere . Egyptian blue synthesis requires the firing of a mixture of a copper salt, calcium carbonate, and quartz usually with a small amount of a sodium flux to temperatures between 850 and 1,050 . Frit cakes of the pigment from the 2nd Millenea BCE from Egypt have been studied by Hatton et al, and these cakes would be ground to produce the pigment with large particle sizes reported to be as large as 150 μm.…”

“…Two experimental methods have recently been reported for the production of the pigment described by Johnson‐McDaniel et al: The melt‐flux method requires lower temperature (875 °C) and produced smaller sized particles in the laboratory (5–15 μm crystallites by SEM), whereas solid state synthesis yielded larger particle sizes (15–50 μm) but requires higher synthesis temperatures (1020 °C), thus above the melting point of bronze. In archaeological studies, Grifa et al demonstrated that high temperatures were achieved in synthesis using crucibles from Cuma, thus exceeding the thermal stability of cuprorivaite crystals (950–1050 °C), thus within the range for both synthesis routes.…”

Paläo‐inspirierte Systeme: Haltbarkeit, Nachhaltigkeit und bemerkenswerte Eigenschaften

“…Außergewöhnliche chemische Kreativität wurde aufgewendet, um Pigmente und Farbstoffe für Farben zu produzieren, die nur selten als stabile Verbindungen in der Natur auftreten. Die Suche nach Alternativen für die teuren blauen Pigmente Lapislazuli, Indigo und Azurit ist besonders anschaulich und führte zu der sehr frühen und innovativen Entwicklung von chemischen Synthesen: Ägyptisch Blau, Han‐Blau, und Maya‐Blau, Cobaltmineralien und –gläser (Cobalt und Coelinblau, Cobaltglas), türkisfarbenes Elfenbein und, in jüngerer Zeit, das Eisencyanid Preußischblau, Phtalocyanine bis hin zum zeitgenössischen International Klein Blue. Ein besonderer Grad an “Perfektion” hinsichtlich der optischen Eigenschaften wurde durch die inspirierenden frühen chemischen Synthesen erreicht, die für die gegenwärtige Materialchemie von besonderem Interesse sind .…”

“…Die Suche nach Alternativen für die teuren blauen Pigmente Lapislazuli, Indigo und Azurit ist besonders anschaulich und führte zu der sehr frühen und innovativen Entwicklung von chemischen Synthesen: Ägyptisch Blau, Han‐Blau, und Maya‐Blau, Cobaltmineralien und –gläser (Cobalt und Coelinblau, Cobaltglas), türkisfarbenes Elfenbein und, in jüngerer Zeit, das Eisencyanid Preußischblau, Phtalocyanine bis hin zum zeitgenössischen International Klein Blue. Ein besonderer Grad an “Perfektion” hinsichtlich der optischen Eigenschaften wurde durch die inspirierenden frühen chemischen Synthesen erreicht, die für die gegenwärtige Materialchemie von besonderem Interesse sind . Ein ähnlich interessantes Beispiel sind frühe islamische Glasuren, die überall für ihren goldenen Schimmer bekannt sind, der durch eine Optimierung der Oberflächenplasmonenresonanzeffekte von Kupfer‐ und Silbernanopartikeln erhalten wird, die an der Glasuroberfläche gebildet werden .…”