Yellow Pigment Powders Based on Lead and Antimony: Particle Size and Colour Hue

Abstract

This paper reports the results of particle size analysis and colour measurements concerning yellow powders, synthesised in our laboratories according to ancient recipes aiming at producing pigments for paintings, ceramics, and glasses. These pigments are based on lead and antimony as chemical elements, that, combined in different proportions and fired at different temperatures, times, and with various additives, gave materials of yellow colours, changing in hues and particle size. Artificial yellow pigments, based on lead and antimony, have been widely studied, but no specific investigation on particle size distribution and its correlation to colour hue has been performed before. In order to evaluate the particle size distribution, segmentation of sample data has been performed using the MATLAB software environment. The extracted parameters were examined by principal component analysis (PCA) in order to detect differences and analogies between samples on the base of those parameters. Principal component analysis was also applied to colour data acquired by a reflectance spectrophotometer in the visible range according to the CIELAB colour space. Within the two examined groups, i.e., yellows containing NaCl and those containing K-tartrate, differences have been found between samples and also between different areas of the same powder indicating the inhomogeneity of the synthesised pigments. On the other hand, colour data showed homogeneity within each yellow sample and clear differences between the different powders. The comparison of results demonstrates the potentiality of the particle segmentation and analysis in the study of morphology and distribution of pigment powders produced artificially, allowing the characterisation of the lead and antimony-based pigments through micro-image analysis and colour measurements combined with a multivariate approach.

Portable Spectroscopic Techniques for the Non-invasive Identification of two historical yellow pigments: Applications and Practical Challenges

“…However, it is well known that the spectral trend of reflectance curves depends on the chemical composition of material, therefore FORS spectra are useful references for the identification of these two pigments, though the interpretation of spectra relating to the colour fields in works of art is often not immediate for example due to the mixture of the pigments itself with others, such as black or white ones, or due to degradation processes. All these factors can cause a variation of the spectral trend, a shift of the curve or a variation of its intensity [9]. XRF spectra give the immediate information on the nature of the pigments.…”

“…Watin in 1773, placed the origin of NY to Naples, Italy, as a manufactured colour or naturally formed mineral found near the sulphur mines on Mount Vesuvius [8]. In addition, it is well-know that the so-called Naples yellow, especially if prepared according to the recipes (such as those of Giovanni Battista Passeri or Valerio Mariani da Pesaro [5,9,10]), is composed of Pb, Sb but also Na or K and that the Pb2Sb2O7 compound is not stable [11] or other compounds not well-characterised containing K [9]. With respect to these facts, Pb-containing yellows are considered suitable for dating and for tracing back to a specific geographical location of an art work.…”

“…In the case of Raman spectroscopy, fluorescence emission due to some organic components could covering the signals of the pigments. Parameters such as the raw materials used for their preparation or the processes of production, but also the type of binder used or degradation processes affects of some properties of pigments such as the color, making them similar, and consequently difficult to discriminate through FORS spectra and chromaticity coordinates [9]. Here, Total Reflectance FT-IR (TR-FTIR) and Fiber Optical Reflectance Spectroscopy (FORS), X-Ray Fluorescence (XRF) and Raman Spectroscopy are used for the non-invasive characterization of the two yellow pigments in combination with X-Ray Diffractometry (XRD) as micro-invasive technique in order to emphasize the importance of a combined use of several analytical techniques, as well as the main advantages and drawbacks of each technique.…”

Colours of the Tijomel ceramic manufacture (1941-1992): characterisation of a set of ceramic colourants and glazed tiles from Decormel Materials Catalogue

“…The elemental analysis of the ceramic colourants 10W and 27H showed a high concentration of Pb, Sn and Sb (Table 3), with lead antimonate (bindheimite) identified by XRD before and after firing. The reflectance spectra of these samples, with sample 10W as an example in Figure 6, present the corresponding band gap at around 530 nm (the middle point), which is typical of this type of pigment [13,[44][45]. Lead antimonate yellow (Pb2Sb2O7), also known as Naples yellow, is an ancient synthetic pigment that has been produced since antiquity in Middle Eastern ceramic and glass manufacturing [46].…”