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Mortar Analysis

Event ID 1106566

Category Recording

Type Mortar Analysis

Permalink http://canmore.org.uk/event/1106566

NJ 23091 65852 An ongoing programme of landscape, buildings and materials analysis is being carried out at Spynie Palace within the framework of this project. Preliminary buildings analysis at Spynie Palace highlighted that several upstanding structures displayed constructional mortar materials in continuous core, bed and coating contexts, and suggested that all of these materials could be broadly characterised as wood-fired limestone-lime mortars. More focused analysis of several different phases in the SE and W range, however, suggested these materials could be divided into two types, with contrasting limestone, temper and fuel compositions which broadly correlated with building phasing. This included: Type A wood-fired limestone-lime mortars which displayed low limekiln relict concentrations and were generally associated with the earliest structural phases in the Curtain Wall and E Gate; and Type B limestone-lime mortars which displayed high kiln relict concentrations, including a ‘cokey’ fuel of unknown provenance, and were associated with secondary contexts in the SE tower and S and W ranges. These on-site characterisations informed a sampling programme, designed to enable further lab-based investigation of these materials, and the assemblage ultimately included: 18 relict fuel inclusions from various mult-phase masonry contexts, 4 mortar fragments, and 2 relict limestone clasts.

Lab-based analysis of the assemblage included petrographic thin section examination of all mortar and limestone samples. This confirmed that all sampled contexts were indeed bound with limestone-lime mortars, and (with the possible exception of the E gate) these lime source materials were texturally consistent with limestone samples collected from local outcrops. Temper sources were also broadly similar across the three constructional mortar samples, with the coating sample presenting the only significantly contrasting temper profile. Rare marine shell inclusions noted during building survey suggest these materials were quarried from a shoreline source, although this evidence was not noted in finer sections. Microscopic examination of relict fuel samples indicated that the assemblage was completely dominated by wood-charcoal, and that the ‘cokey’ evidence noted during building analysis was the result of fuel vitrification.

Archive: NRHE (intended)

Funder: University of Stirling and Historic Environment Scotland

Mark Thacker – University of Stirling

(Source: DES Volume 19)

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