Terahertz Analysis of Quinacridone Pigments

Squires, Andrew; Kelly, Michael; Lewis, R. A.

doi:10.1007/s10762-016-0333-2

Cited by 12 publications

(9 citation statements)

References 18 publications

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“…A commercial beeswax medium (R & F Handmade Paints) was used to bind the pigment powder into a paint. Our previous work has shown white beeswax transmits well in the terahertz spectral region . White beeswax is decolorized by mechanical filtration, not chemical bleaching.…”

Section: Methodsmentioning

confidence: 94%

“…These investigations confirmed that the lowest-frequency modes are ∼1.5 THz. (Further details are given in our previous work …”

Section: Methodsmentioning

confidence: 99%

“…Recently, terahertz techniques , have begun to be applied to the analysis of art work. − Both conventional and panel paintings have been studied in this way. , Artists’ materials are now being examined in greater detail . These materials include pigments, such as seven red mineral pigments used in ancient Chinese artworks and, most recently, quinacridone . However, the studies to date have been largely phenomenological, simply presenting “signatures” of various materials without fundamental understanding.…”

Section: Introductionmentioning

confidence: 99%

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Distinguishing Quinacridone Pigments via Terahertz Spectroscopy: Absorption Experiments and Solid-State Density Functional Theory Simulations

et al. 2017

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Through a combined experimental and theoretical investigation we determine that the fundamental modes of three quinacridones fall in the terahertz spectral range (1-10 THz, ∼30-300 cm). In each spectrum the terahertz resonances correspond to wagging, rocking, or twisting of the quinacridone rings, with the most intense absorption being an in-plane rocking vibration of the carbonyl oxygens. In spite of these spectral similarities, we demonstrate that terahertz measurements readily differentiate β-quinacridone, γ-quinacridone, and 2,9-dimethylquinacridone. The spectrum of β-quinacridone has a group of closely spaced modes at ∼4 THz, whereas in contrast the spectrum of γ-quinacridone displays a widely spaced series of modes spread over the range ∼1-5 THz. Both of these have the strongest mode at ∼9 THz, whereas in contrast 2,9-dimethylquinacridone exhibits the strongest mode at ∼7 THz. Because quinacridones are the basis of widely used synthetic pigments of relatively recent origin, our findings offer promising applications in the identification and dating of modern art.

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Section: Methodsmentioning

confidence: 94%

“…These investigations confirmed that the lowest-frequency modes are ∼1.5 THz. (Further details are given in our previous work …”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Distinguishing Quinacridone Pigments via Terahertz Spectroscopy: Absorption Experiments and Solid-State Density Functional Theory Simulations

et al. 2017

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“…This fingerprinting capability of terahertz spectroscopy is highly advantageous in efficient identification of ancient and modern pigments. Consequently, a number of representative pigments, such as azurite, − malachite, − , verdigris, , and magenta, , have been extensively studied in the terahertz range, and a few spectral databases have been established at various institutes around the world . However, in these data sets, most often, only transmission spectra are given, which include rather distorted spectral features of individual absorption lines.…”

Section: Introductionmentioning

confidence: 99%

Terahertz Spectroscopic Analysis of the Vermilion Pigment in Free-Standing and Polyethylene-Mixed Forms

Lee

Kim

et al. 2021

ACS Omega

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Terahertz spectroscopy can be utilized as an effective nondestructive identification tool for the study of artist's pigments. Consequently, extensive measurements have been conducted on representative pigment species, and a few terahertz spectral databases have been constructed. However, the reported spectra were often acquired from pigment samples mixed with polyethylene at room temperature with low resolution, which often led to low-quality spectra with unresolved overlapping lines further broadened due to thermal effects. Here, we present our study of vermilion (HgS, mercury sulfide) as an illustration of how we can overcome such difficulties by studying free-standing oil-paint samples at room temperature and then by performing low-temperature measurements on polyethylene-mixed samples to minimize line broadening due to thermal effects. Our results identify clearly resolved absorption peaks due to lattice vibrations of vermilion at 40.4, 44.5, and 89.9 cm −1 at 2 K. The temperature dependence of the peak shift and line broadening reveals anharmonic characteristics of these lattice vibrational modes. Our approach will definitely suggest new ways to improve and enhance existing terahertz spectral databases of ancient and modern pigments toward actual analysis, diagnosis, and conservation of heritage artworks.

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“…132−135 Following these early demonstrations, the utility of this approach was apparent and led to applications spanning biologically relevant molecules, 102,103,110,136 illicit drugs, 137−140 pharmaceuticals, 8,141−143 explosives, 144−146 and pigments. 147,148 Specifically, because of the dependence of terahertz vibrations on some of the weakest intermolecular forces found in crystals, the successful reproduction of low-frequency vibrational spectra implies that the forcesnot only the weak forces but, by extension, all forcesare well-modeled, lending significant confidence to the theoretical model. This can be illustrated with an OH bond, wherein if the interactions of that bond are incorrectly modeled, then subsequently all related forces will likely be flawed, ultimately yielding a poor terahertz spectral simulation.…”

Section: ■ Introductionmentioning

confidence: 99%

Advances in Low-Frequency Vibrational Spectroscopy and Applications in Crystal Engineering

Kleist

Ruggiero

2021

Crystal Growth & Design

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The field of low-frequency vibrational spectroscopy has grown significantly over the past two decades, based on advances in both experimental lasers and optics, as well as highperformance computing and quantum mechanical simulations. The combination of these techniques has enabled unprecedented insight into the atomic-level dynamics that occur at terahertz frequencies, which usually involve large-amplitude motions of entire molecules. This has ultimately provided the community with new tools for investigating and engineering crystalline materials through an understanding of intermolecular forces, as well as dynamics. In this Perspective, an overview of the field will be provided and complemented by recent examples where lowfrequency vibrational motions are being used to understand, and drive, bulk material function.

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Terahertz Analysis of Quinacridone Pigments

Cited by 12 publications

References 18 publications

Distinguishing Quinacridone Pigments via Terahertz Spectroscopy: Absorption Experiments and Solid-State Density Functional Theory Simulations

Distinguishing Quinacridone Pigments via Terahertz Spectroscopy: Absorption Experiments and Solid-State Density Functional Theory Simulations

Terahertz Spectroscopic Analysis of the Vermilion Pigment in Free-Standing and Polyethylene-Mixed Forms

Advances in Low-Frequency Vibrational Spectroscopy and Applications in Crystal Engineering

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