Green Chitosan:Thiourea Dioxide Cleaning Gel for Manganese Stains on Granite and Glass Substrates

Abstract

The cleaning or removal of manganese stains on Cultural Heritage has not been much tested or successful so far. The aim of this article was to assess a new green cleaning gel for Mn-rich black-blue stains on different substrates. The black-blue stains were characterized at optical and chemical level through RGB data, colorimetry, optical microscope, FTIR, XRF and XPS. Mn-stained granite found on historical churches at Vila Real (North of Portugal) and glass jars of Leclanché cells, belonging to the ISEP’s Museum (Portugal) collection, were the ideal case studies to test the efficiency of Chitosan:Thiourea Dioxide (TD) cleaning gel. TD proved to be the best candidate to reduce insoluble manganese oxides, over Hydroxylamine Hydrochloride and Hydroxymethanesulfinic Acid. Cleaning assays performed on stained granite samples collected at a historical quarry and in situ application on stained granite churches showed the complete removal of the stains. Similar results were obtained on stained glass jars. This article presents an innovative, feasible and green Chitosan gel embedded with TD and phosphoric acid, applied to the cleaning of Mn-stained granite and glass substrates.

Building Granite Characterisation, Construction Phases, Mason’s Marks and Glyptography of Nossa Senhora de Guadalupe Church, Mouçós e Lamares, Galicia-North Portugal Euroregion

“…Granite is the most used stone in Galicia-North of Portugal for historical constructions, especially in churches (Barroso and Oliveira 2020; Campos et al 2021a, b). The recovery of traditional stones involves the study of their historical quarries and their characterisation with petrographic and petrophysical techniques, which allow scientists to establish the degree of decay and durability of building stones (Fort et al 2013;Forestieri et al 2017;Zalooli et al 2020).…”

Chemistry of Sodium Hydroxymethanesulfinate and Thiourea Oxides: New Data

“…Хитозановый гель с добавками ДОТМ с успехом использовался для очистки поверхности памятников и стен церквей от пятен, содержащих оксиды марганца [30]. Диоксид тиомочевины переводит нерастворимые соединения Mn(IV) в растворимые соединения Mn(III) и Mn(II), причем более эффективно, чем гидроксиламин гидрохлорид и гидроксиметансульфинат.…”