In this thesis, the behaviour of artificially produced brown patinas in simulated atmospheric conditions was investigated. Four different kinds of patinas were prepared and analysed: oxide patina, electrochemical patina, sulphide brown patina in two layer thicknesses and the so-called “French brown” patina. The purpose of this work was to explain which factors affect the sensitivity of such patinas to environmental influences.
The patinas were prepared by heating, electrochemically or by applying potassium sulphide and ferric nitrate solutions to Cu10Sn bronze samples. Their colour, as well as their thickness and compactness, determined by metallographic analysis, were compared. Electrochemical measurements of open circuit potential, linear polarisation and potentiodynamic measurements were carried out in a simulated solution of urban rain, in order to determine their resistance to advancing corrosion. The results were compared with unpatinated bronze sample. Samples with thinner and thicker layers of sulphide, “French brown” and electrochemical patina were exposed to the solution of artificial rain for a period of 44 days. Before exposure, after 14, 30, and 44 days the patinas’ colour was checked visually, and the morphology and chemical composition of corrosion products were analysed.
All prepared patinas were brown to grey in colour. They differed in thickness, morphology and chemical composition. Three characteristic morphologies were observed: cracks, fine corrosion products, and flakes. The electrochemically prepared patina proved to be the most stable, while the “French brown” patina was the most susceptible for further corrosion. The “French brown” patina was the only one on which green patina had formed in the shape of well defined brochantite crystals within 44 days in the simulated urban rain solution. After this period, most of the original brown patina was covered by brochantite while both sulphide patinas and the electrochemical patina remained unchanged.
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