Data di Pubblicazione:
2012
Citazione:
STUDI PER LA MODELLIZZAZIONE DELLA RIFLETTANZA SPETTRALE NEGLI STRATI PITTORICI / D. Pandini ; tutore: P. Johnson, N. Ludwig ; coordinatore: M. Bersanelli. Universita' degli Studi di Milano, 2012 Jan 20. 24. ciclo, Anno Accademico 2011. [10.13130/pandini-davide_phd2012-01-20].
Abstract:
Nowadays a lot of physical techniques are available in order to have information about an historical painting. They are able to know which chemical elements are present in the paint layer, or they are also able to show the pattern under the colored layer, but there is not a non-destructive technique able to study the artist technique of painting or the historical pigments used in order to obtain the particular nuance we can observe.
In this thesis we study an evolution of the VIS-NIR-spectroscopic technique with these goals. In particular we start from a preliminary historical study of the artist’s pigments available for paintings and, starting from the colorimetric technique till the spectrophotometetric technique we create a representative pigments Database and we study a new method for pigment grindings identification, pigment’s mixture recognition and pigments layer technique studies.
The international method for color measurements provides the use of colorimeter but the sizes of these instruments don’t allow to perform measurements in any cases. Applications in the field of cultural heritage like as pigment characterizations on statues or ceramic and sometimes paintings don’t allow the use of integrating sphere. So we study the applicability of optical fiber for the realization of optical fiber remote probes. The use of optical fibre is consolidated for spectroscopy measurements (in particular for UV-VIS-NIR spectroscopy), but it may introduce an error in the detection of the spectra and, in consequence, a further error in the definition of the color of the sample analyzed. The first goal of this work was therefore the evaluation of compatibility of CIE colorimetric results obtained using Fiber Optic Reflectance Spectroscopy (FORS) and those values obtained with a standard colorimeter and then we extend the use of remote probe in NIR range for the measure of the pigments reflectance spectra.
After the test of the remote probe setup we have studied spectra obtained for well-defined mixtures of the most important artist’s pigments with the barium sulphate white pigment, the same used like standard sample for color measurements. These mixture simulate the different desaturation degree of the main color like in the earlier paintings techniques before Renaissance age. In order to have the best numerical characterization we fit the main behavior of the spectra using two analytical models: the Gaussian function (with 4 free parameters) and the sigmoidal function (with 4 free parameters): the comparison of their parameters allow to define the change of the spectra for different concentration of each colored pigment in the white one when thy were mixed in oil or without oil (as in oil renaissance paint technique and in the tipical affresco Middleage paint technique). Determination of weight mixture Pigment to white were: pigment pure, 1:1, 1:2, 1:5, 1:10, 1:20, 1:50. The pigments analyzed with sigmoidal fit were: Cadmium Red , Lacca rossa (Red Laquel), Chromium Orange, Cadmium Yellow, Naple Yellow (with Lead), Green Chromium oxide, Cobalt Blue, Cobalt Violet and Ultramarine Green. Pigments studied using Gaussian fit were: Green Chromium oxide, Cobalt Violet, Ultramarine Green, Verderame (Copper Green), Azurite, Ultramarine blue (artificial), Lapislazuli, Green earth, Malachite Green, Zinc Yellow and Cinabrum.
The next step is the research of a model able to study mixtures of two different colored pigments. The best historical model able to describe the interaction light-pigment was the Kubelka-Munk theory. In this model the Absorbtion (K) and Scattering (S) coefficients are needed. Here we study a method to obtain this coefficient from the reflectance spectra of the pigments and the spectra of their mixtures with barium
Tipologia IRIS:
Tesi di dottorato
Keywords:
reflectance ; pigment ; painting ; colorimetry ; FORS ; Kubelka-Munk ; scattering coefficient ; absorbtion coefficient ; azurite ; copper green ; prussian blue ; pigment layer ; pigment powder ; pigment grinding ; spectrophotometer ; remote probes ; colorimetric values ; pigment mixtures ; Canaletto ; spectrum ; glaze ; gaussian spectrum fit ; sigmoidal spectrum fit ; pigment color ; pigment tint ; optical fiber ; colorimeter
Elenco autori:
D. Pandini
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