Atmospheric corrosion of fire-gilded bronze: corrosion and corrosion protection during accelerated ageing tests

Abstract

Fire-gilded bronze (replicating the materials of Lorenzo Ghiberti’s Paradise Door (Baptistery of Florence, 1452)) was aged in runoff/stagnant conditions by accelerated exposure tests in synthetic acid rain. After preliminary electrochemical investigations, a detailed characterization of gilded bronze samples before and after artificial ageing tests followed. Surface and cross-sections analyses were performed by FIB/FEG-SEM, SEM/EDS and micro-Raman spectroscopy. The protective efficiency of a coating based on 3-mercapto-propyl-trimethoxy-silane was also quantitatively assessed by GF-AAS through analysis of metal release, while the aesthetical appearance of coated and uncoated gilded bronze before and after ageing was evaluated by colour measurements

Surface investigation of naturally corroded gilded copper-based objects

“…Cu or Ag, as substrates to produce fire-gilded or silvered objects instead of Cu-based or Ag-based alloys, and avoided to recasting a miscellany of objects typical of craftsmen with poor technological skills [1,377,[64][65][66][67]. All thisese information confirms the instructions of Theophilous [38], which that suggested the use of pure copper or Cu-based alloys low in tin and lead to carry out the fire-gilding process [1,7,[64][65][66][67]69]. Indeed, the presence of copper alloying elements like Sn, Pb and Zn could play a detrimental role during the thermal processes, due to the possible undesired selective oxidation at the interface between the silver or gold-rich layer and copper substrate [1][2]12,[24][25][26].…”

“…Recently, two papers have been published [6][7] which reporting the characterisationtics of fire-gilded bronze replicas carried out by using different analytical techniques such as synchrotron radiation photoemission (HR-SRPES), glow discharge optical emission spectroscopy (GD-OES), scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM+EDS), micro-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The fire-gilded replicas have been were prepared by adopting ancient methods and using a quaternary (Cu-Sn-Pb-Zn) alloy as a substrate and then aged with "synthetic" rain at pH = 4.3 in order to simulate unsheltered exposure to rainwater (runoff conditions) with a total time of wetness (TOW) of 30 days [6].…”

Metals and Environment: Chemical Outputs From the Interaction Between Gilded Copper-Based Objects and Burial Soil

“…The 3D distribution of the molecular ion species was used to correlate degradation products with changes in the sample multilayer structure. In the last decade, only a few works considered corrosion mechanisms and products in ancient gilded artifacts similar to those here reported (Ingo et al, 2013;Chiavari et al, 2015;Masi et al, 2016), among which an even shorter number of studies employed SIMS technique (Lechtman, 1984;De Ryck et al, 2003) providing also results about depth profiling (Yin et al, 2008;Ingo et al, 2018). On the other hand, the majority of the literature regards corrosion in non-gilded artifacts, studies in manufacturing techniques or studies on gilding of different, non-metallic artworks (Schreiner and Grasserbauer, 1985;Hackea et al, 2004;Adriaens, 2005;Dowsett et al, 2005;Van Ham et al, 2005;Bonaduce et al, 2007;Balta et al, 2009;Sandu et al, 2011;Tortora et al, 2014;Biocca et al, 2016;Di Tullio et al, 2016;Iorio et al, 2019).…”

Inclusion of 5-Mercapto-1-Phenyl-Tetrazole into β-Cyclodextrin for Entrapment in Silane Coatings: An Improvement in Bronze Corrosion Protection

“…Concerning the environments where the coating protectiveness was assessed, the cyclic acid rain (AR) spray test was performed using a synthetic AR, prepared with Sigma-Aldrich ACS reagents, according to the recipe reported in [34] and containing the following ion concentrations: −1 , and pH 4.35. During the electrochemical tests, accelerated corrosion conditions were obtained by using tenfold concentrated AR (ARX10, pH = 3.3) at 30 °C.…”