Organoclays were prepared by cation exchange reaction from
The EDXRF spectrum of the dark blue colored plaster is given in Fig. 11. The key elements Al, S, Si appeared in the EDXRF spectrum of the dark blue colored sample No 4, are characteristic of an ultramarine blue pigment (Na8–10Al6Si6O24S2–4). Unfortunately reliable detection of Na by spectro iQ-II model EDXRF spectrometer cannot be performed. The FTIR spectrum shows very specific vibrational bands that EPZ-6438 can be used as markers related to the silicate group. The observed band at 1010 cm−1 is assigned to the (Si–O–Si) antisymmetric stretching mode, whereas the band at 450 cm−1 is related to the (O–Si–O) deformation mode (see Fig. 3b). The 728–560 cm−1 region of the FTIR absorption spectrum of the blue colored plaster is given in Fig. 12, in comparison with its second derivative profile. The calcite (712 cm−1) ultramarine blue (694 cm−1)  and gypsum (669 and 602 cm−1)  bands are clearly observed. The other characteristic bands of ultramarine blue at 666 and 584 were inferred from the second derivative profile ,  and .