Terahertz Analysis of Phthalocyanine Pigments

• Published in: Journal of infrared, millimeter and terahertz waves Vol. 40; no. 7; pp. 738 - 751
• Main Authors: Squires, A. D., Lewis, R. A.
• Format: Journal Article
• Language: English
• Published: New York Springer US 15-07-2019; Springer Nature B.V
• Subjects: Art restoration; Art works; Classical Electrodynamics; Color; Conservation; Copper; Electrical Engineering; Electronics and Microelectronics; Engineering; Free form; Instrumentation; Investigations; Nondestructive testing; Photovoltaic cells; Pigments; Spectroscopy; Spectrum analysis; Substrates; Thin films; Time domain analysis; Spectroscopy; Phthalocyanine; Pigment; Art; Artwork; THz; Terahertz; Paint; Painting
• ISSN: 1866-6892; 1866-6906
• DOI: 10.1007/s10762-019-00599-9

In situ, non-invasive and non-destructive analysis of important artworks and cultural pieces is largely important in art conservation science. Terahertz time-domain spectroscopy and imaging delivers these requirements but lacks a materials database with fundamental understanding of salient pigments, binders and substrates. In this study, the most important synthetic pigments, the copper phthalocyanines, are investigated through terahertz time-domain spectroscopy. The terahertz spectrum reveals a series of characteristic modes in a 0.1–3-THz range across 14 pigment samples. Identification and distinction of copper phthalocyanines’
α
,
β
and
𝜖
crystal polymorphs is demonstrated. This uniqueness within the terahertz regime is extended to two halogenated variants and a metal-free form. This invites the use of THz spectroscopy in investigation of contemporary artworks, post 1935, containing these pigments and promotes applications such as identifying fraudulent works of art.