ETD system

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Tesi etd-01132014-142623

Thesis type
Tesi di dottorato di ricerca
The role of tannin-based dyes in the degradation of historical textiles: a multiple analytical approach
Settore scientifico disciplinare
Corso di studi
correlatore Dott.ssa Degano, Ilaria
controrelatore Prof.ssa Pérez-Arantegui, Josefina
tutor Prof.ssa Ribechini, Erika
Parole chiave
  • Organic dyes
  • GC-MS
  • Degradation
  • Tannins
  • Wool
Data inizio appello
Riassunto analitico
Historical textiles are an important part of our cultural heritage. Such textiles are subject to several types of degradation that damage their integrity and readability. Historical textiles are affected by fading, yellowing and loss of material. Thus, their readability is often difficult and sometimes impossible.
In the last few years a number of studies on textile degradation and conservation have investigated the chemical processes causing fibre deterioration in order to propose durable conservation methods.
Historical textiles can be damaged by the way the fabric was used, by the original dyeing procedure, and by the conservation conditions. Textile dyeing is one of the principal causes of fibre damage and thus the effects have been widely studied. Thus textile conservation is an extremely challenging task.
Of the widespread range of dyeing techniques and materials used to date, iron-tannin dyestuffs are known to cause specific and intense damage to textiles, highly affecting the fibre integrity. This specific class of black dyestuffs is classified as mordant dyestuffs, due to the fact that they are applied using metal salts, called mordants, to bound tannin molecules to the fibre. Iron salts are largely used as mordants to create brown-black complexes, but also other metals were used, such as aluminium and copper.
The deterioration of black textiles is a widespread problem. Several examples of textiles dyed with this kind of colorant suffer from severe degradation effects, which in most cases are much stronger than those acting on fibres subjected to the same conservation conditions but dyed with other dyestuffs. Several studies have focused on the reasons for the weakness of the tannin dyed fibres, however the answers obtained are still insufficient to develop conservation or restoration methods to arrest degradation . Starting from the well-known mechanism of iron-gall ink corrosion, oxidation and hydrolysis reactions are presumed to act on the fibres. Unfortunately, there are fundamental differences between inks and dyestuffs in terms of the method of application and treatment. Inks were also applied mainly to polysaccharide matrices, while tannin dyestuffs were commonly used in dyeing of proteinaceous fibres, such as wool or silk.
This PhD research is part of a project, “VAT, The short life of tannins”, which is being funded by the regional administration in Tuscany, Italy (PAR FAS 2008-2013). The aim of the project is to understand the chemical processes acting on textiles dyed with tannin dyestuffs. This thesis focuses on the degradative effects of tannins on wool threads. The final goal of this work will be the creation of a predictive model for describing the ageing processes that affect fibres.
A multi-analytical approach will be used employing complementary techniques to investigate the tannin-fibre complex. Specifically, three different research lines will be followed:

• investigation of wool matrix degradation
• characterization of the composition of tannin dyestuffs
• investigation of mordant oxidation state and structure

Chromatographic, mass spectrometric and spectroscopic techniques will be used. Gas Chromatography-Mass Spectrometry (GC-MS) and High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) will be used to investigate wool matrix degradation, Direct Exposure Mass Spectrometry (DE-MS) and High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) will be used to characterize dyestuffs composition, and Synchrotron based spectroscopies will be used to obtain information regarding iron mordants. Scanning Electron Microscopy combined with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) will also be used to gain information on both the wool matrix and metal mordant.
The results will be used to develop innovative analytical protocols and to create a database of chemical properties . The resulting ageing model will be validated by analyzing samples collected from several historical tapestries and fabrics.