Old is Gold: The Guimarães Carpets

Between 2010 and 2011, TTT members Jessica Hallett, Raquel Santos and Cátia Frade were involved in the study of three Persian carpets from the Palace of the Dukes of Bragança collection in Guimarães (Portugal). The objects’ high quality was recognized together with the advanced state of degradation, with previous interventions causing greater damage. An interdisciplinary team comprising textile conservators, art historians and conservation scientists was gathered to develop an innovative approach with surprising results.  

In 2007 the three ‘Salting’ carpets were discovered at the Palace of the Dukes of Bragança, in the city of Guimarães. Two are prayer rugs with central niches, while the third has a central medallion. Finely knotted in wool on a silk foundation, and embellished with metal threads, this is the largest collection of these carpets known outside the Topkapi Saray (Istanbul).

The term ‘Salting’ comes from the name of the famous collector, George Salting (1835-1909), who gave a notable example to the Victoria & Albert Museum in 1909, which was originally attributed to 16th-century Iran. However, the vivid colours of this and other carpets, and the existence of similar examples in the Topkapi, led historians to argue later that they were Turkish rugs from the 18th or 19th centuries, and possibly even forgeries of classical Persians carpets.

This discovery was a unique opportunity, not only to reflect upon the problems of origin and date, but also to take the advantage of using scientific tools to obtain responses that might be hidden on the carpets' materials. As a result analyses were conducted on the fibres, dyes, mordants and metal threads used to make the three Guimarães carpets. This data was then compared with published results for related examples documented in the literature to determine whether they were 1) products of Persian or Turkish workshops, and 2) from the classical period (16th to 17th centuries), or later, from the 19th or 20th centuries.

Clockwise: Benguiat prayer rug; Duff prayer rug; Medallion carpet
Woven structure of the carpets, showing warps, wefts, knotted pile and metal thread.


HPLC-DAD results of lac dye red source.

Fibres • Dyes • Metal threads

Fibre analysis confirmed wool and silk in the knotted pile and foundation, and the Medallion Carpet was found to have an extremely high knot count (ca. 11,155 knots/dm2). All colours were analysed, and a more detailed study was applied to the reds. Lac-dye (Kerria spp.) was identified and, as this is the predominant dye of the red ground of classical Persian carpets, it appeared to offer a possible clue to their provenance.


Therefore, the first High Performance Liquid Chromatography-Diode Array (HPLC-DAD) database of lac-dye insects (Kerria and Paratachardina genera) was created with the support of Principal Component Analyses (PCA) - statistical analysis. Historical insect sources (87 samples) from the Royal Botanic Gardens, Kew (London), as well as other entomological sources, were analysed and compared with historical textile samples taken from the Guimarães carpets. These preliminary results revealed that probably the red dye is related with insect sources from Pakistan or a nearby region. Narrowing their provenance further requires more rigorous taxonomic study of the wide variety of insect species known to produce lac-dye, followed by chemical analysis and comparison with a wider range of carpets. Together, the results from all colours analysed reveal the presence of a high quality classical Persian palette.


Scanning Electronic Microscopy (SEM-EDX) revealed a distinctive method of manufacture of the metal threads, involving a hand-cut silver lamina of fine gauge, covered with a gold coating and twisted around a silk core. This is consistent with the method previously proposed by some authors for the ‘Saltings’ and ‘Polonaise’ carpets. Finally, AMS Radiocarbon dating confirmed a date between the late 15th- and mid-17th century for the Medallion Carpet, excluding the possibility of either a late date or forgery. Overall the data pointed to a 16th- or 17th-century date, and Iran as the place of manufacture for the carpets. Moreover, the detail knowledge of the carpets’ materials attained ways to develop a responsible and effective further treatment.


Cleaning • Support • Consolidation

Being exhibited directly placed on the floor and without any protective surface (such as a vitrine), the carpets acquired an overall dust layer, especially in the knotted-pile surface. Widespread oxidation of the metal threads and the presence of an external dark-grey layer composed of silver corrosion products were also observed. Exhibition beneath a window, in direct sunlight and uncontrolled environmental conditions was probably the main cause for fading of the colours. Considerable material loss and fragility was observed, especially in the longitudinal and transversal axes. 

The poor condition of the three Guimarães carpets, and their exceptional value, raised several conservation challenges. Achieving physical and chemical stability and increasing their visual aesthetic were the main goals. The partial supports were removed from the carpets without any noticeable material loss. Then, suction-table wet cleaning resulted in a better extraction of dirt particles, pH increase, colour improvement, and preservation of metal threads. Consolidation with hand stitches contributed to reinforce the carpets structure, as well as the use of a textile support.

After conservation, several efforts were made in order to establish adequate preservation measures, such as limited exhibition time and horizontal display under a vitrine, which will allow both dust and UV light protection. Hence, the carpets could then be returned to the exhibition gallery. Certainly, the results from this collaborative project were so inspiring that, in 2011, the carpets were formally classified as National Treasures by the Portuguese Ministry of Culture.




Medallion carpet fading (detail).
The Guimarães Carpets after conservation treatment: Benguiat prayer rug; Duff prayer rug; Medallion carpet.


Santos, R., Sousa, M. M., Hallett, J., Sarraguça, J., Oliveira, M. C., Simmonds, M. S. J., Nesbitt, M. 2015. “Analysis of Kerria and Paratachardina Genera Using HPLC-DAD, MS and Multivariate Data Analysis for Identifying Lac-dye Sources in Historical Textiles”, Dyes and Pigments, 118, pp. 129-136.
Santos, R. and Hallett, J. 2014. “Interwoven knowledge: The understanding and conservation of three Islamic carpets” in A. Gerritsen and G. Riello (eds), Writing Material Culture History, pp. 257-264. London: Bloomsbury Publisher Ltd.
Santos, R. and Hallett, J. 2012. “Três Tapetes Encontrados no Paço Ducal”, Chapter of the Paço Ducal de Guimarães Museum Catalog.
Frade, C., Cruz, P., Lopes, E., Sousa, M., Hallett, J., Santos, R., Aguiar-Ricardo, A., Casimiro, T. 2011. “Cleaning classical Persian carpets with silk and precious metal thread: conservation and ethical considerations”, ICOM-CC 16th Triennal Conference, Lisbon, 19-23 September, Lisbon, International Council of Museums.
Santos, R. 2010. The discovery of three lost ‘Salting’ carpets: Science as a tool for revealing their history. Master dissertation, New University of Lisbon, Portugal.