11 Hoiseşti L11 - white pigment Raman spectra - Romanian Database of Raman Spectroscopy
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Buzgar N., Apopei A. I., Buzatu A. (2009) - Romanian Database of Raman Spectroscopy (http://rdrs.uaic.ro)


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Alexandru Ioan Cuza UniversityFaculty of Geography and Geology

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11 Hoiseşti L11

Sample image with white pigment
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Raman spectrum of white pigment - Raman spectrum of Quartz
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Legend: white pigment______ and quartz______ Download Raman spectrum of quartz standard .spc or .txt
Raman spectrum of white pigment - Raman spectrum of Rutile
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Legend: white pigment______ and rutile______ Download Raman spectrum of rutile standard .spc or .txt
Interpretation of the white pigment Raman spectra

The Raman spectra of the white pigment are defined by background noise (BN) and strong fluorescence (F). The lack of any Raman bands, even weak ones, is due to a kaolinite clay. Constantinescu et al. (2007) have shown through XRD studies that the white pigment is a light clay (type kaolin), but the same authors mention Ca as the major chemical element in the white pigment (kaolinite clay has a low concentration of Ca, the main elements being Si and Al). Calcium carbonate is certainly absent from the white pigment, because it has a good Raman signal, at least at 1087 cm-1 (Buzgar and Apopei, 2009).

However, the large number of spectra acquisitions on the white pigment allowed the detection of some minerals in the kaolinite clay, quartz and TiO2 (rutile and, rarely, anatase). The presence of quartz is indicated by the Raman band at ~465 cm-1, which is the most intense line of quartz. The other Raman bands are hidden by the BN&F.

Rutile gives a good Raman signal, even when it apears as very fine crystals. For this reason, the presence of rutile in the white pigment is obvious, based on the two specific Raman bands (Buzgar et al., 2009).

The presence of TiO2 in the white pigment on artefacts was indicated by Middleton et al. (2005). The analysis of a sample of white paint from a ceramic pot of Roman age, using FT-Raman spectroscopy, indicated that a component of the white paint was anatase.

An issue is the high frequency of appearance of rutile in relation to anatase. We believe that almost all artefacts made of fine ceramics from Hoiseşti were fired at ~900°C, which determined the transformation of anatase into rutile. Another argument which supports this theory is that the black raw ceramics from Hoiseşti present artificial white temper, made of small quantities of white kaolinite clay, where anatase and certainly not rutile is present. Moreover, in this case, the firing process was conducted below 700-750°C (above this temperature, black carbon is destroyed).

The presence of quartz and TiO2 in the kaolinite clay may suggest that the clay used as white pigment has a residual nature, formed by the weathering of igneous rocks. Clay deposits of this kind are very rare and generally occur near volcanic neogen sites (Parva and Cornăiţa - Bistriţa Năsăud region; Haita, Pietrosul and Stejar Valleys – Suceava county).

We believe that the anatase-rich kaolinite used as white pigment during the Roman age (Middleton et al., 2005) is of the same genetic type, many sources of kaolinite clay formed by weathering occuring on the territory of the Roman Empire.

References

• BUZGAR N., BODI G., AŞTEFANEI D., BUZATU A. (2010) - The Raman study of white, red and black pigments used in Cucuteni Neolithic painted ceramics. Analele Stiintifice ale Universitatii “Al. I. Cuza” - Iasi, Tome 56, issue 1 [link]

• BUZGAR N., APOPEI A. I. (2009) - The Raman study on certain carbonates. Analele Stiintifice ale Universitatii “Al. I. Cuza” - Iasi, Tome 55, issue 2, 97-112 [link]

• Middleton, A.P. , Edwards, H.G.M., Middleton, P.S., Ambers, J., 2005. Identification of anatase in archaeological materials by Raman spectroscopy: implications and interpretation. Journal of Raman Spectroscopy, 36, 984-987.