Abstract
The literature on the application of Multispectral and Hyperspectral imaging for identification of pigments on artworks is sparse. While these methods do not provide the analytical capability that spectroscopies do offer, the use of spectral imaging has the advantage of being a rapid and relatively low-cost solution for the examination of large areas. This paper presents a flowchart for the identification of historical pigments applied with gum Arabic using multispectral imaging (wavelength ranging from 360 to 1700 nm) performed with a modified digital camera for infrared, visible and ultraviolet photography; and an InGaAs camera for infrared reflectography. The flowchart method will be most successful on paint made of one layer of pure pigment, and it can selectively discriminate only a fraction of the 56 pigments analyzed. Though, considerably limited in its analytical capabilities, the low cost and speed of the workflow make the method worthwhile, even if only to localize retouching and areas appearing the same hue but painted with different pigments. The InGaAs camera is the only expensive instrument used in this study but its cost is relatively affordable for the average painting conservation studio since only a model with a low pixel count is required (320×256 pixels) rather than a more sophisticated InGaAs scanner system.
Highlights
Multispectral imaging (MSI) [1,2] and Hyperspectral Imaging [3,4,5,6], have been suggested as methods for the non-destructive identification of pigments
The intention of this paper is to show that with a flowchart based methodology it is possible to tentatively identify some historical pigments by means of MSI performed with simplified equipment and without the aid of imaging analysis software
Unlike other references, which suggest the use of software algorithms to analyze the MSI images, this paper proposes a more straightforward method based on visual examination and the use of a photoediting software for the characterization of features apparent in the image
Summary
Multispectral imaging (MSI) [1,2] and Hyperspectral Imaging [3,4,5,6], have been suggested as methods for the non-destructive identification of pigments. Cadmium red is identified for its exceptionally bright IRF, for mineral pigments the composition is likely to be relatively consistent, and with organic lakes there could be variation in the composition; such as the case with the nine madder lakes varieties produced by Kremer (product codes 37202, 37203, 37217, 37218, 372051, 372052, 372057, 372058, 372142) They were all tested and 372051 was chosen for this flowchart since the fluorescence exhibited under UV254 illumination was the most representative when compared with the madder lakes previously documented in literature [32,33,34,35], Figure 13. Retouching 2 is characterized by its intense UVF which is due to its binder, while retouching 1 is differentiated from the original blue (likely azurite) because is bright in the IR
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