Formation of Metallic Mercury During Photodegradation/Photodarkening of α‐HgS: Electrochemical Evidence

Abstract

Das rote Pigment α‐HgS neigt in Gegenwart von Licht und Chloridionen zur Schwärzung. Als Grund für die Zersetzung und Entfärbung werden die Bildung von (schwarzem) β‐HgS oder Quecksilbermetall vermutet, doch diese Substanzen wurden noch nicht auf natürlich oder künstlich zersetzter HgS‐Farbe nachgewiesen. Elektrochemische Experimente belegen nun die Bildung von Quecksilbermetall in Gegenwart von Licht und Chloridionen.

Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light

“…14,15 Electrochemical techniques have been proposed as alternative methods for a fast monitoring of the degradation mechanism of a series of photodegraded semiconductor pigment powders. 16,17 Despite the general characterization and distribution of photo-degraded compounds that have been established in these studies, neither exhaustive information on the wavelengthdependence of the alteration process of pigments nor experimental evidence in how different types/doses of visible light may inuence the pathways of the formation of specic secondary compounds have been provided.…”

Thermodynamic and experimental study of the degradation of the red pigment mercury sulfide

“…Recently, the formation of metallic mercury from HgS by the joint action of light and chloride ions has been experimentally demonstrated by means of electrochemical methods. 46,47 While electrochemistry is a very efficient way to detect metallic mercury, it is unfortunately not directly applicable to the study of tiny original painting fragments. Indeed, the non-invasive identication of metallic mercury with micrometric resolution and in the presence of a complex mixture of different Hgcompounds 48 is not easy to accomplish.…”

Photodegradation mechanisms and kinetics of Eosin-Y in oxic and anoxic conditions

“…In addition, chromatographic studies were undertaken to identify secondary products. Recently, amperometry and voltammetry have been proposed as alternative means of studying the photodegradation process of inorganic pigments [19,20]. These electrochemical methods allowed to monitor the photodegradation of pigments in-situ and to clarify their photodegradation mechanism and kinetics under different environmental conditions.…”