7/27/2023 0 Comments Remove bronze patina![]() ![]() Bronze disease, along with similar visual conditions caused by other moieties, remains an active area of research within object conservation. However, re-exposure of the object to even atmospheric water can restart the process. Deprived of water, the reaction cannot continue. Initial treatment can involve placing the object in a desiccating environment. It is the presence of two different white and green salts that lead to the fuzzy green appearance. The reaction then repeats from equation (3). The cuprous ion reacts with the chloride ion in the hydrochloric acid to form the insoluble white colored salt cuprous chloride: The remaining copper is oxidised by air to the cuprous ion: The cuprous chloride reacts with atmospheric moisture and oxygen to form a green cupric chloride/cupric hydroxide compound and hydrochloric acid: The cuprous ion reacts with the chloride ion to form the insoluble white colored salt cuprous chloride: Initially, copper is oxidized to the cuprous ion: In many cases chlorides may be present within the interior of the artefact the disease may reoccur if not isolated from water and/or oxygen. Ĭhlorides may occur in or on the metal due to contamination from soil, water (especially seawater), the atmosphere, human sweat, or be present as impurities when the object was created. When an artefact is recovered, surface encrustations may hide and/or protect bronze disease. Absence of dissolved chlorides and oxygen in the soil means buried objects may not be affected while interred (similarly, lack of soluble salts and oxygen means that buried metals may not develop a patina or that oxidation of the metal may be reversed). Coastal areas may also be hazardous due to salt carried in the atmosphere as well as the humidity. īronze disease is common or even ubiquitous on artefacts recovered from a marine environment due to the presence of chlorides in seawater. These treatments may also remove any patina, loss of which is often seen as undesirable to collectors and conservators but is preferable to loss of the object. Treatment for the condition typically involves physical removal of the chlorides (through scrubbing), chemical or electrochemical removal, and then isolating the object from oxygen, water, and future chloride contamination using an airtight container or a wax coating. Īs it relies upon the presence of chlorides, water, and oxygen, the absence of one of these three halts the progress, although any damage done is irreversible. ![]() Unlike bronze disease, verdigris serves to protect the metal. These properties are all in comparison with verdigris, which is normally a duller shade, uniform across the whole of the affected object, and cannot be scratched off with wood or fingernails. The patches of bronze disease can be scraped off the surface using a fingernail or a wooden pick. Bronze disease typically affects isolated patches of the object in severe cases being a visibly and tactilely raised bloom of microscopic crystals as well as being associated with pitting. It is commonly present in all colors in this range due to the series of reactions that cause it and there may also be tiny, possibly microscopic, blue crystals. īronze disease ranges from vivid green to pastel green. It is not reserved for antique objects but can affect contemporary metals like modern cupro-nickel coins. Despite its name, bronze disease can affect any copper-bearing alloy, not just bronze. It is contagious in that the chlorides which cause it can spread the condition if they are brought into contact with another cuprous object. It was originally thought to be caused by bacteria. Description īronze disease is the chloride corrosion of cuprous (copper-based) artifacts. Transfer of chlorides from the contaminated artefact to other artefacts can spread the condition. Treatment is very difficult, costly and not always effective. If not treated, complete destruction of the affected artifact is possible. It is not a bacterial infection, but the result of a chemical reaction with the chlorides that usually occurs due to contamination of the bronze object by saltwater or from burial in specific types of soil where chloride salts are present. It can occur as both a dark green coating, or as a much lighter whitish fuzzy or furry green coating. Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys.
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