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Fibers and Polymers 2013, Vol.14, No.9, 1581-1585
1581
Studying Irradiation Homogeneity in Light Aging for Historical Textile
Conservation
Khaled Elnagar*, Sameh M. Reda1, Harby E. Ahmed
2, and Shady Kamal
Textile Metrology Lab, National Institute for Standards, Alharam, Giza, Egypt1Radiometry Lab, National Institute for Standards, Alharam, Giza, Egypt
2Faculty of Archeology, Cairo University, Giza, Egypt
(Received January 27, 2012; Revised March 3, 2013; Accepted March 10, 2013)
Abstract: Instrumental light aging is one of the most important tools for restoration and conservation of historical textiles. Itused in testing stability of conservation materials, in addition to its lightening effect during the presentation in the museums.Light fading is an important tool for preparing the aged textile and other polymeric samples especially for archaeologicalconservation applications. Many fadometers do not give homogeneous exposure for all sample’s areas. This work studies thecolor changes of silk fabric dyed with turmeric (Curcuma longa L.) mordanted with alum or ferric sulfate. Color change wasstudied for the exposure periods ranged from five to hundred hours. Three positions of different irradiance levels weremeasured on the same sample namely (bottom, middle and upper). Individual color change for each position was recordedand studied. The results showed that there is non-homogeneous irradiance distribution due to different positions in fadometeror mordant used.
Keywords: Light aging, Conservation, Silk, Mordant, Turmeric
Introduction
Developing and understanding of the causes and mechanisms
of light fading of historical textile fibers dyed with natural
dyes in museums have been the subject of substantial
researches over the past 50 years [1-4]. The sensitivity of a
particular dye depends upon the chemical structure of the
dye. The fading process is rather complicated in practice
because of oxygen which is involved in the process. It is a
matter of the energy of the radiation and the absorption of
the particular dye as well as the way in which the dyed
material may be protected by other chemical substances that
make the dyed material more fast to light [5-9].
The Illuminating Engineering Society (IES) defines
Illuminants as relative spectral power distributions consisting of
ultraviolet (UV), visible (VIS) and infrared spectral (IR)
energies [10]. Visible spectrum is a small amount of energy
ranges from 380 nm to 780 nm. UV energy ranged from
100 nm to 400 nm. IR energy ranges from 0.78 µm to 103 µm.
Lighting an object involves the narrow band of wavelengths
ranged from approximately 380-780 nanometers, Light is
accompanied by small amounts of Infrared (IR) and
Ultraviolet (UV). It is important to note that light contributes
to vision and damage, whereas non-visible IR and UV
contribute to damage, but not to vision. A simple formula
puts the exposure effects into consideration.
Light → radiant energy → damage to objects
“When radiant energy is incident on the surface of a
material, a portion of that energy is absorbed promoting two
different processes: radiant heating effect and/or photochemical
action [11].
Most of light fading and colour testing equipment are
based on using daylight illuminant (D65) that corresponds to
a mid-day sun in Western Europe/Northern Europe; hence it
is also called a daylight illuminant. As any standard
illuminant (it is represented as a table of averaged spectro-
photometric data), any light source which statistically has
the same relative spectral power distribution (SPD) can be
considered a D65 light source. The name D65 suggests that
the correlated color temperature (CCT) should be 6500 K.
There are no actual D65 light sources, only simulators can
be used [12-14]. The correlated color temperature (CCT) is a
specification of the color appearance of the light emitted by
a lamp, High pressure mercury lamps are widely used in the
fading process [15].
This work aimed to study the homogeneity of irradiation
for some silk fabric dyed with turmeric (Curcuma longa L.)
natural dye mordanted with alum or ferric sulfate. The
samples were assessed with respect to the color parameters
and color difference in addition to light intensity at different
irradiation positions in fadometer.
Experimental
Fabric
Greek silk fabric supplied by TSIAKIRIS Co., Soufli-
Greece. The fabric was indentified in Table 1.
Turmeric dye (Curcuma longa L.), and of color index
(C.I.) 75300, or “Natural Yellow 3” was purchased from the
Egyptian local market.
Mordents such as alum AlK(SO4)2·12H2O and ferric
chloride FeCl3 were supplied by Fluka.*Corresponding author: [email protected]
DOI 10.1007/s12221-013-1581-6
1582 Fibers and Polymers 2013, Vol.14, No.9 Khaled Elnagar et al.
Dyeing
Dye Extraction
Turmeric roots were grinded into a fine powder, and
soaked in water (10 % w/v) for 24 h. and followed by
heating to boil for two hours. with continuous stirring. It
may require adding water to compensate the evaporated
water during the heating process. Finally allow the extract to
be cooled then filtered many times to get a clear colored and
transparent solution.
Dyeing Procedure
The dyeing was performed by the simultaneous dyeing
and mordanting technique [16]. In this method a liquor ratio
(LR) of 1:20 was used (For 1 g of good we use bath volume
of 20 ml). 10 grams of degummed silk fabric were used as
protein fiber substrate. The dyeing experiments were performed
in beakers according to the temperature-dyeing diagram
given in Figure 1. Liquor ratio (LR) was adjusted to be 1:20.
Mordants namely alum AlK(SO4)2·12H2O and ferric chloride
FeCl3 concentrations were adjusted to give a final concen-
tration of 0.5 % (owf). After dyeing, the unfixed dyestuff
was removed by rinsing three times with cold water (5 min,
room temperature, LR 1:20) [17-21].
Light Aging Instrument (Phadometer)
The samples in fading machine (phadometer) showed in
Figure 2.
The light source used was Mollar lamp 500 W self-ballasted,
Mix-light, Fluorescent coated. The separation between the
vertical axis of the lamp and the cylinder carrying the
samples is 33 cm. The UV irradiance level in µW/cm2 at
different sample positions measured using National Institute
for Standards (NIS) reference radiometer UDT 268-UVA
whose maximum spectral responsivity is located at 365 nm.
Also the total spectral power distribution of the lamp
measured using NIS grating monochromator (Newport
77000) resulting in 7.2 % of the output of the lamp is UVA
(315-400 nm) as CIE color system definition.
Color Measurement
The CIE-Lab. values of the color changes were measured
using double beam Optimatch spectrophotometer (Datacolor
international Spectraflash SF450-UK). The colors are given
in “Commission International de l'Eclairage” (CIE) Lab
coordinates, (L) : brightness (100=white, 0=black), (a) : red-
green coordinate (positive sign=red, negative sign=green),
and (b) : yellow-blue coordinate (positive sign=yellow, negative
sign=blue) [22,23].
L*=116(Y/Yn)1/3−16 (1)
a*=500[(X/Xn)1/3−(Y/Yn)1/3] (2)
b*= 200[(Y/Yn)1/3−(Z/Zn)1/3] (3)
∆E* = {(∆L*)2 + (∆a*)2 + (∆b*)2}1/2 (4)
Where Xn, Yn and Zn of the not-irradiated samples before
light aging. Y, X and Z are the color coordinates of the
samples at every irradiation period. These equations were
used in the spectrophotometer software to calculate the color
differences.
Results and Discussion
Spectral Distribution
The spectral power distribution specifying the lamp used
in this work is described in Figure 3. It is measured by NIS
facility of spectral power distribution system based on single
monochromator Newport model 77700.
The spectral distribution of the lamp clarify that the lamp
emits power at wide spectrum from ultraviolet to infrared.
The lamp output is 8.0 % ultraviolet, 48.0 % visible, and
43.0 % near infrared. The regions responsible for the most
Table 1. Fabrics structure of Silk dyed fabric that used in experimental part
Samples Thread (cm) Mechanical parameter [24] Weight
(g/m2)Weaving structure
Warp Weft Tensile force (kg·f) Elongation (%)
Uncolored silk 32 25 27.967 15.85225.4
Plain weave
1\1Silk-Turmeric 32 25 25.959 12.821
Figure 2. Schematic diagram of the illumination areas in the
phadometer (lamp located in the center of cylindrical shape).
Figure 1. Temperature time diagram of the one-bath dyeing process.
Light Aging Fibers and Polymers 2013, Vol.14, No.9 1583
detoriations in the sample are found to be the UV and IR
regions.
Irradiance Homogeneity
The irradiance levels in µW/cm2 at three positions top,
middle and bottom for the 12 samples positions of the fading
machine were measured using NIS reference radiometer
268-UVA. Figure 4 shows non-homogeneous relation between
the average levels and the positions indicating that the
highest irradiance level in our case (≈31,000±403 µW/cm2)
while the lowest irradiance level was (≈28,000±616 µW/
cm2) obtained at the top of the sample. This finding may be
attributed to the lamb configuration and irradiance distribution
of the bulb in addition to the lamp temperature inhomogenity.
The color difference of three locations on the same
samples was calculated at different exposures' time and it
was clear that the middle position on the samples showed the
maximum deterioration. This can be attributed to the fact
that of the inverse relationship between distance of
illuminant to the sample and the intensity as stated in the
following inverse square law [25].
Where E is irradiance and I is Light intensity.
For better fastness to light and washing, the use of
mordants may be essential for most of natural dyes. The
function of the mordant is to assist the adsorption of the dye
and promote good bonding of dye and fiber as a bridge,
which helps to bond fiber and natural dyes at the molecular
level [15]. In this work two mordants were used namely Fe
and Al mordants. The studied two mordants show different
photofading responses of the turmeric dyeing. Figures 5 and
6 show that the sample mordanted with alum is sensitive to
its position inside the fadometer than those of iron mordanted
samples [26,27]. Aluminum salt produces lower light stability
than ferric salt. This result may be attributed to the capability
of aluminum salt to form weak coordination complexes with
the dye, leading to quite strong bonds with the dye but not
with the fiber. Thus they block the dye and reduce its
interaction with the fiber [15].
Data in Table 2 shows the effect of the exposure period on
the studied phadometer at three different positions studied
for silk fabric samples dyed with turmeric dyes mordanted
with alum. Lightness value ‘L’ for all studied positions
(bottom, middle and top) is increased with the increase of
exposure time and this can be attributed to the degradation of
the chromospheres in the turmeric dye. Values of the red-
green component ‘a’ show changes from green to red
(hypsochromic shift with shorter exposure period of 10 hours
EI
r2
----=
Figure 3. Spectral power distribution of 500 W Mix-light Mollar
lamp.
Figure 4. Relation between the irradiance levels and their
locations on the sample compartment.
Figure 5. The color difference for different exposure time for
turmeric natural dye mordanted with Alum.
Figure 6. Color difference (∆E) for different exposure time for
turmeric natural dye mordanted with ferric mordant.
1584 Fibers and Polymers 2013, Vol.14, No.9 Khaled Elnagar et al.
maximum. Extended exposure period of the samples shows
more reddish color (bathochromic shift). Value of yellow
blue component indicates that the sample colors are shifted
to less yellow [28,29]. Data in Table 3 show that by increasing
the exposure period, brightness value ‘L’ increased and the
yellowish brown sample’s color decreased. Red -green
component ‘a’ values shifted to green color component. This
can be attributed to the molecule transitions to a shorter
wavelength due dye degradation and low stability of the
curcumin molecules (Figure 7) to day light. It is well known
that the dye on drying conditions turned to keto chemical
form, this chemical structure change accompanied with
colour changes depend on the extension of the light
exposure periods from 0 to 100 hours [29,30].
Conclusion
In conclusion, it can be seen that silk fabrics dyed with
Turmeric dye mordanted with different mordants are
affected by the position (Irradiance homogeneity) in the
phadometer and in turn the irradiation homogeneity. All
interested conservation and metrological textile scientists
should be aware that the location of the tested samples inside
the fadometer must be taken into consideration in addition to
type of mordant used the light ageing conditions (e.g., the
illumination source and its spectral power distribution) as
well as its distance to the tested samples. To achieve a
uniform light radiation of a light guide, it is very useful to
use a diffuser front of the radiating side. With a diffuser foil
a uniform and vectored radiation is achieved.
Acknowledgements
The work was performed at Textile Metrology and
Radiometry laboratories in the National Institute for Standards,
Giza Egypt. The authors wish to thank Eng. Rasha Sadek
Table 2. Color parameters (L), (a) and (b) for the three positions on the same samples dyed with turmeric natural dye and mordanted with
Alum after exposure periods in phadometer
Exposure
period (hour)
Top position Middle position Bottom position
L (a) (b) L (a) (b) L (a) (b)
0 79.53 -1.35 57.46 78.31 -0.91 58.02 78.86 -1.86 61.26
5 78.32 1.16 38.61 78.29 0.78 38.27 71.24 2.41 49.81
10 80.06 1.12 30.34 80.16 1.24 29.65 80.35 0.92 28.47
20 81.24 1.05 24.93 81.78 1.19 24.07 81.54 0.77 22.92
40 81.87 0.76 25.63 81.73 0.78 25.63 82.06 0.49 24.28
60 83.18 0.27 21.71 83.14 0.36 21.83 83.34 0.14 20.47
80 82.99 0.35 21.82 83.32 0.32 21.63 83.76 0.14 20.13
100 82.44 0.11 21.06 82.37 0.07 20.85 83.50 -0.05 19.67
Tables should be followed by their keys (e.g., L for lightning, a red-green, b yellow-blue).
Table 3. Color parameters L, a and b for the three positions on the same samples dyed with turmeric natural dye and mordanted with Ferric
sulfate after exposure periods in phadometer
Exposure
period (hour)
Top position Middle position Bottom position
L (a) (b) L (a) (b) L (a) (b)
0 80.57 1.50 63.07 80.38 1.08 62.33 80.42 0.30 63.65
5 81.24 2.27 37.35 82.19 1.76 37.24 41.89 2.61 -23.47
10 82.93 1.92 27.18 82.63 1.96 27.02 83.25 1.60 26.61
20 84.04 1.14 22.77 83.55 1.25 22.84 84.31 1.05 22.55
40 84.49 0.79 23.70 84.16 0.81 23.43 83.62 0.75 23.43
60 85.55 -0.04 21.07 85.12 0.14 21.20 84.46 -0.04 20.74
80 85.35 -0.02 21.02 85.25 0.05 20.90 85.11 -0.06 20.35
100 84.32 -0.26 21.17 84.04 -0.23 20.38 83.59 -0.26 20.01
Tables should be followed by their keys (e.g., L for lightning, a red-green, b yellow-blue).
Figure 7. Curcumin in Turmeric keto- and enol forms.
Light Aging Fibers and Polymers 2013, Vol.14, No.9 1585
from textile metrology Lab., for her contribution in the
experimental part.
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