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|Title: ||Influence of mordants in the colour of natural dyes: theoretical predictions and experimental results|
|Authors: ||Costa, Cristina|
Estêvão Candeias, A. J.
Palace Carvalho, A. J.
Prates Ramalho, J. P.
|Keywords: ||Natural dyes|
ZINDO-INDO/S Semi-empirical calculations
|Issue Date: ||Apr-2007|
|Abstract: ||Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile
production and a cultural heritage that urges to preserve. The richness of colours displayed by some of the
Arraiolos tapestries denotes the likely use of a wide variety of dyes. The different light-fastness of dyes
combined with the use of different types of mordants can also explain the appearance of pale shades and
fading in some tapestries due to different molecule interactions with the support fibres.
The work we present is part of a major project (experimental and theoretical) that envisages the identification
of the dyes and mordants used throughout the ages in the production of Arraiolos tapestries and the
establishment of the major factors (like mordant, humidity and light) that are responsible for the colour and
fading of the natural dyes as well as for the degradation of the fibres.
It is well known that the colour of a dye depends on the type of mordant used, due to the formation of metal
complexes that cause a change in the molecular orbitals energies and hence a shift in UV/Vis absorption
The electronic structure and transitions in the visible spectra of some dyes and mordants identified on
Arraiolos rugs were predicted by the ZINDO-INDO/S semi-empirical molecular orbital method [1,2] in
order to identify the origin of the colours and characterize the influence of metal coordination on colour
modifications. The molecular geometry of each dye-mordant complex was optimized at DFT level using the
Gaussian03 package  and a simulation of the UV/Vis absorption spectrum was calculated using ZINDO.
Another important outcome of this study was the determination of the chromophore properties of fragment
molecules produced by the dyes degradation processes that enabled the evaluation of the colour changes of
the dyes and subsequent fading.
Wool fibres were dyed with previously identified natural dyes and mordants and the colour parameters and
the spectra were determined using a UV-Vis portable spectrometer. These parameters were compared with
the results from the theoretical predictions.|
|Appears in Collections:||QUI - Comunicações - Em Congressos Científicos Internacionais|
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