23 Hoiseşti L11 - red 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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23 Hoiseşti L11

Sample image with red pigment
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Raman spectrum of red pigment - Raman spectrum of Anatase, Quartz and Hematite
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Interpretation of the red pigment Raman spectra

The red pigment studied contains hematite and, more frequently, quartz. The Raman spectra recorded on fine sherds from Hoiseşti and Scânteia are very similar and present the main bands of hematite. The diffuse shape of the Raman bands is caused by the fine granulation of hematite. Also, this is confirmed by high intensity peaks in the 200-300 cm-1 region and a low intensity at 1320 cm-1, which is the most intense Raman band of hematite in large crystals (Zoppi et al., 2008; Buzgar et al., 2009).

The presence of quartz is proved by the most intense band at ~465 cm-1

Quartz gives a Raman signal which is more intense than that of hematite, therefore hematite bands are less obvious in the Raman spectra.

The presence of both hematite and quartz in the red pigment excludes the use of Fe oxyhydroxides as pure red pigment. For the red color, red clay, washed several times, a process that enriched the clay with Fe oxyhydroxides (+quartz), was used. This known process is used even nowadays by pottery artisans. The source of this clay is not a special issue, as it is commonly found interbeded throughout sedimentary deposits of the Moldavian Platform.

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]

• 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.

• Zoppi, A., Lofrumento, C., Castellucci, E.M., Sciau, Ph., 2008. Al-for-Fe substitution in hematite: the effect of low Al concentrations in the Raman spectrum of Fe2O3. Journal of Raman Spectroscopy, 39, 40-46.