A Multiwavelength Approach for the Study of Contemporary Painting Materials by Means of Fluorescence Imaging Techniques: An Integration to Spectroscopic Methods

Margherita Longoni,Marco Gargano,Alessia Buttarelli,Silvia Bruni

doi:10.3390/app12010094

Abstract

Imaging methods based on visible luminescence induced by ultraviolet (UV) radiation are well consolidated in the investigation of ancient works of art, to map varnishes, retouches, and possibly some pigments. As far as contemporary art is involved, the wide range of synthetic materials, especially pigments, introduced from 1850 onwards, makes the possible application of the technique particularly challenging. Among the colouring substances used by artists in the 19th and 20th centuries, only cadmium-based pigments received attention due to their typical near-infrared luminescence. Nevertheless, the fluorescence emission exhibited by several synthetic pigments upon visible excitation was recently demonstrated and confirmed using UV radiation in the present work. The subsequent possibility of individuating such materials in paintings by ultraviolet fluorescence (UVF) images was explored on mock-up painting samples of a wide series of pigments dispersed in oil or acrylic binder. Visible and infrared luminescence images obtained by irradiating with visible radiation (VIVF and VIL) were also collected. It was thus evidenced the possible advantage of the choice of a different excitation wavelength in discriminating between the contributions of pigment and binder. Finally, a recent oil painting on panel was also examined as case study.

Highlights

The synthetic in in thethe present work are are listed in Table
Could be demonstrated that some pigments, widespread in contemporary artists’ colcolours, are characterised by a strong emission, allowing for their observation ours, are characterised by a strong emission, allowing for their observation in in the corresponding ultraviolet fluorescence (UVF) images. This is the case of quinacridone magenta and violet the corresponding UVF images. This is the case of quinacridone magenta and violet PR122
Within the series of of colouring compounds here examined by imaging techniques, it was not possible to colouring compounds here examined by imaging techniques, it was not possible to observe pigments belonging to the families of naphthol AS reds, benzimidazolone orange and yellow, and acetoacetic arylide yellows

Summary

Introduction

Visible luminescence induced by UV radiation has been a wellknown and widely exploited phenomenon since the 1930s [1,2,3,4,5,6,7]; long wave UV-A lamps (365 nm emission peak) are traditionally used to non-invasively map the distribution of varnishes, retouches, and in some case for the preliminary mapping of specific pigments. The traditional approach consists in using the 365 nm excitation band and recording the visible luminescence to what is seen by the eyes in the direct examination. Thanks to the relatively short wavelength of the UV radiation with an intrinsic limited capacity in the penetration of lower painting layers, fluorescence is mainly used in the examination of external layers, constituted more often by varnishes than by binders and pigments

Methods

Results

Conclusion