Electrochemical Photodegradation Study of Semiconductor Pigments: Influence of Environmental Parameters

Abstract

Chemical transformations in paintings often induce discolorations, disturbing the appearance of the image. For an appropriate conservation of such valuable and irreplaceable heritage objects, it is important to have a good know-how on the degradation processes of the (historical) materials: which pigments have been discolored, what are the responsible processes, and which (environmental) conditions have the highest impact on the pigment degradation and should be mitigated. Pigment degradation is already widely studied, either by analyzing historical samples or by accelerated weathering experiments on dummies. However, in historic samples several processes may have taken place, increasing the complexity of the current state, while aging experiments are time-consuming due to the often extended aging period. An alternative method is proposed for a fast monitoring of degradation processes of semiconductor pigments, using an electrochemical setup mimicking the real environment and allowing the identification of harmful environmental parameters for each pigment. Examples are given for the pigments cadmium yellow (CdS) and vermilion (α-HgS).

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.…”

Zur Photochemie von Künstlerfarben: Strategien zur Verhinderung von Farbveränderungen in Kunstwerken

“…[16][17][18] In Blumen in blauer Vase von Va nGogh wurden amorphes CdSO 4 ,CdC 2 O 4 und PbSO 4 in der veränderten, gräulichen Kruste identifiziert. [20] Computersimulationen der Wechselwirkung von CdS mit O 2 und/oder H 2 Oz eigten, dass Strukturdefekte (d. h. Cd/S-Leerstellen) an der Pigmentoberfläche gut in Einklang sind mit den komplexen Photooxidationsreaktionen, die in Gemälden festgestellt werden. [17] Bereiche mit Cd-Cl-Verbindungen angereichert waren (Abbildung 2b,c,e-g).…”

“…[18] Die Photooxidation von CdS-basierten Verbindungen zu CdSO 4 -d er wahrscheinlichste Abbauweg in der Gegenwart von O 2 und Feuchtigkeit [19] -w urde durch elektrochemische Messungen an CdS-Pulver bestätigt. [20] Computersimulationen der Wechselwirkung von CdS mit O 2 und/oder H 2 Oz eigten, dass Strukturdefekte (d. h. Cd/S-Leerstellen) an der Pigmentoberfläche gut in Einklang sind mit den komplexen Photooxidationsreaktionen, die in Gemälden festgestellt werden. [21] Dennoch sind wir weit entfernt von einem tiefgreifenden Verständnis der Reaktivitätv on CdS in Farbschichten, aus den folgenden Gründen:1)Sowohl CdSO 4 als auch andere Verbindungen, die als Folgeprodukte identifiziert wurden, kçnnten bereits in den ursprünglichen Farbformulierungen als Überbleibsel der Synthese oder als Additive vorhanden gewesen sein.…”

Raman, X‐Ray Fluorescence Spectroscopies and Graphene Oxide Modified Screen Printed Electrodes to Identify the Pigments and Earth Present in Ancient Leather Samples

“…XRF can give information on single elements belonging to the investigated objects, but their native redox status -which could help in the attribution to a specific compound -are completely unknown. The detection of the redox status [7] is strictly related to the chemical composition of the original pigments and represents an important and interesting challenge in Cultural Heritage applications. The knowledge of the chemical composition allows to select treatments/solvents suitable for restoration without interfering with the stability of the pigment and, consequently, with its colour.…”