REDISCOVERING THE ARRAIOLOS TAPESTRIES - ANALYSIS OF NATURAL DYES AND FIBERS IN HISTORICAL SAMPLES

Abstract

Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile heritage. It is difficult to date the beginning of the production of rugs in Arraiolos, but they were already produced in the late 1600’s as they are listed in the inventories of Portuguese aristocratic households in the beginning of the 18th century. This study is integrated in project “REMATAR- Rediscovering the Materials of Arraiolos Tapestries” (PTDC/HAH/64045/2006) which intends to obtain systematized information on the composition, structure and degradation processes of these tapestries, and to use this data to improve conservation methodologies. The gathered data on natural dyes and mordants used in tapestries dated from different periods will hopefully allow the establishment of a time scale of materials usage. The tapestries studied belong to the Museu Nacional de Arte Antiga (MNAA) which the most complete and representative Arraiolos collection. Wool, linen and hemp were the most important fibres used in the making of Arraiolos tapestries. The richness of colours displayed by some of the Arraiolos tapestries denotes the likely use of a wide variety of dyes. However, only a few dye sources used worldwide to dye wool are described in the few bibliographic reports on Arraiolos making. Dye identification is usually done by extraction of the dyed fibre followed by high performance liquid chromatography with diode array detection (LC-DAD) and coupled with mass spectrometry (LC-MS) analysis of the extract. Scanning electronic microscopy (SEM), techniques enable the comparison of the fibers length, thickness, cross section and surface analysis. SEM combined with energy-dispersive x-ray analysis (EDX) can be used to give information on degradation processes and also on the mordants. Several procedures are available in the literature to extract dyes from wool and a study was performed to evaluate which is the most adequate for the different classes of natural dyes. Samples taken from a 17th century rug (nr 88 from the MNAA collection, dimensions 294x168cm) were extracted using optimized developed extraction procedures and analyzed by LC-DAD and LC-DAD-MS in order to identify the natural dyes. Microanalysis by SEM-EDX and μ-PIXE was done to identify the fibres used and assess their degradation; mordant analysis was done by 2D elemental mapping. The results on the historic samples show that hemp and linnen were used for the support (warp threads) and wool for the weaving. Weld (for the yellows and greens), indigo (for the blues and greens) and cochineal (for the reads) were used to dye the wool fibres. Cochineal dye was never referred by Rivara in his reference dye recipe book probably because it describes the Arraiolos manufacture in later periods, when tapestries had lost richness of patterns and colours. In general, the wool fibres display the typical scale structure of wool with no obvious disruptions of morphology. However, in some cases, the wool fibres present roughened surfaces with loss of scale structure, transversal cracking and longitudinal splitting which is indicative of wear and biological degradation. With exception to blue dyed fibres, EDX analysis showed the presence of aluminium (and, in some cases, other metallic minor elements) evenly distributed over the fibres which is consistent to the use of alum as mordant.