Coatings applied on the surface of

Coatings applied on the surface of dyed textiles for protection
must not affect the aesthetic appearance of the treated textile substrate.
To evaluate the effect of the siloxane-nanoparticle coatings
on the appearance of silk, colourimetric measurements were carried
out using the L*a*b* coordinates of the CIE 1976 scale. The
global colour differences (E*) of the silk surface, raised by the
application of a protective coating, was calculated according to Eq.
(1):

where, L*, a* and b* are the brightness (0 for black–100 for white),
the red–green component (positive for red and negative for green)
and the yellow–blue component (positive for yellow and negative
for blue), respectively.
Colourimetric measurements were carried out on undyed silk
and silk dyed with natural dyes, which have been commonly used
and identified in textiles of the cultural heritage, that is indigo
(blue dye), weld, turmeric (yellow dyes) and cochineal (red dye)
[60]. Dyeing recipes applied for the preparation of the samples are
described in the Supplementary file. The E* measurements for the
undyed and dyed silk samples treated with pure siloxane and siloxane
with nanopaticles at different concentrations are summarised
in Table 1. Fig. 7 is provided as an example showing in detail the
measurements corresponding to silk dyed with indigo.
Fig. 7 shows that the application of pure siloxane on silk
dyed with indigo caused a colour change (E* = 3.27 according to
Table 1) that is primarily attributed to the change of the brightness
component (L*). The application of pure siloxane had a similar
effect on the appearances of undyed silk and silk dyed with weld,
turmeric and cochineal, according to the results of Table 1.
The addition of SiO2 nanoparticles in the protective coatings at
the low concentration of 1% w/w had a positive effect, as the E*
values reduced from that of the silk specimens treated with pure
siloxane (Table 1). The colour changes imposed by the application
of siloxane + 1%w/w SiO2 correspond to values lower the JND (Just
Noticeable Difference)limit of 2.3 [48],thus implying thatthe use of
these coatings do not affect practically the aesthetic appearances of
the treated silk specimens. However,the use of more SiO2 nanoparticles
(2 and 3% w/w) in the protective coating results in larger E*
values, according to the results of Table 1.
T

The effect of the SiO2 nanoparticles is more pronounced in silk
dyed with turmeric, indigo and cochineal because the colour coordinates
of these dyes are substantially different compared to the
corresponding valuesmeasuredfor SiO2, according to Table 2.However,
the colour components for SiO2 are relatively close to the
corresponding values reported for undyed silk and silk dyed with
weld (Table 2). Consequently, the effect of the SiO2 nanoparticles
on the colour appearance of these two samples is smaller.
In summary, the results of Table 1 suggest that the use of siloxane
+1%w/w SiO2 for the protection of undyed and dyed silk is
appropriate and does not cause any colour change noticeable by
human eye. At the 2% w/w nanoparticle concentration, the coatings
correspond to higher E* (Table 2) but also to somewhat better
water and oil repellence, evidenced by the results of Fig. 3a and b.