Raman identification of strongly absorbing phases: The ceramic black pigments

To get black decorations requires high ceramic technology and there are different ways of achieving this. Their identification can be very useful to discriminate between different manufactures or periods of production but this information is often very hard to achieve because of their strong absorption of the illuminating laser beam, whatever the wavelength used, causing a very low scattering intensity and, in case of power increase, a transformation of phase which may lead to the misinterpretation of the spectra obtained. We test the use of five instruments with different characteristics (wavelength and power of excitation, spectral resolution, filters and microscope) applied to a group of heterogeneous samples which have in common the presence of a black glaze. The results obtained (manganese oxides, cobalt oxides or a mixture of the two even with the addition of haematite) are compared considering the different methodologies used and leading to a preference towards high-sensitivity rather than high-resolution spectrometers, notch-filtered rather than edge-filtered instruments and microscopic configuration used on freshly created cross-sections. The importance of the objective choice is demonstrated. Small grains may be preferred. The problems encountered in the analysis of dark to black ceramic pigments are discussed. Advantages of high-sensitivity low-cost instruments versus more expensive ones are pointed out. The importance of excitation power control is emphasised. Copyright © 2010 John Wiley & Sons, Ltd.