It is not a bacterialinfection, 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. This is a really interesting choice of topic (maybe I'm biased as a science major though) and well done. The benzotriazole does not remove the chlorides or neutralize the acid present but acts as a physical barrier to water, oxygen, and chlorides and so can be used as a final step in all cases but as a first or only step in only minor cases. [4], Initial treatment can involve placing the object in a desiccating environment. Posted at Dec 14/2007 10:10PM: Storing the object in a completely dry or oxygen free environment will also prevent bronze disease as will isolation from contact with chlorides. I remember your interest in this topic during the Coins and Collections visit. ♦Bronze “disease” is a condition in which the coin produces acid (normally hydrochloric or hydrosulfuric acid) internally, and begins to disintegrate ♦The exterior usually exhibits green or brown “growths” that cover the pitting that acids will create [2], Removal of the chlorides is essential. [2][3], The duration of soaking may be days to weeks or even a year for severely contaminated objects. Telephone: (401) 863-3188 This converts the cupreous ions to elemental copper. This typically involves soaking in acetone to displace any water in the specimen. It’s a nasty bit of business, with no chemical treatments and the ability to kill your tree within 3-5 years. Well, no man-made artifacts can last forever... thanks for new info!. I learned a thing or two! This is commonly referred to as bronze disease and must be taken care of by removing the chlorides before the whole coin eventually disintegrates. Later rinses should be with distilled water though the chlorine of a chlorinated town water supply is likely to have evaporated from tap water inside 24 hours and therefore will not further contaminate the object.[2][3]. ����/��u����%����"+��,���i���*��.��`Q�&���]�=���#C���n��c������*��v�(I�L�#"��Z �5s�-#V9ns�a��5�5/��Gك�ੵ���!�*��gG���S1&��d��XH��^- So which means that after 100 or more so years, they are gonna turn into...dust? Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys. Bronze Leaf disease is a fungus that infects trees in the poplar family, namely Swedish columnar aspen, trembling aspen, and tower poplars. Bronze disease is a type of corrsion which gives antiquities collectors nightmares! [4] Deprived of water, the reaction cannot continue. The sesquicarbonate may remove copper from the artefact as it forms a complex ion with copper. Bleach oxidizes the surface of the copper. This is visible as a blackening or darkening of the copper surface. The oxide may coat the artefact with unsightly but harmless black spots or generally, darken the metal. One chemical treatment is soaking the object in a 5% sodium sesquicarbonate solution. (4) Cu → Cu+ + e−, The cuprous ion reacts with the chloride ion in the hydrochloric acid to form the insoluble white colored salt cuprous chloride: Posted at Dec 11/2007 08:49PM: Follow the Centers for Disease Control & Prevention (CDC) guidelines under “How to clean and disinfect.” There you will find easy-to-prepare bleach or alcohol solutions. '�ס�~zl������CW�0���ۮY��K�4�]��ؾzT��qOӅ�����s�U,����g{u#!��!�yվ Ŧ�iBa����.J����!x|v#��n�%�M���9 d��;�����R����sG�1$�7�1҈"����C7��a���~�Gge%��)!7\ WG_1����n�Y����rze���f�}@:;xL���U���Z�UYpӥi��Y��)�q-�����qp�د-�=�])aא�����+,7��s��?&��)~?>� endstream endobj 9 0 obj 436 endobj 4 0 obj << /CropBox [ 36 36 756 576 ] /Type /Page /Parent 5 0 R /Resources << /Font << /F0 6 0 R >> /ProcSet 2 0 R >> /Contents 8 0 R >> endobj 17 0 obj << /Length 18 0 R /Filter /FlateDecode >> stream Waxes prepared with BTA are available commercially, the idea being that the BTA will prevent any reaction by chelating the surface copper and the wax acting as a physical barrier reducing exposure to water, oxygen, and chlorides. The regular use of disinfectant cleaning products such as bleach has been linked to an increased risk of developing fatal lung conditions, researchers said. Archaeologies of the Greek Past - Home, Joukowsky Institute for Archaeology & the Ancient World Posted at Dec 16/2007 10:16PM: Joukowsky_Institute@brown.edu, Scott, David. Bronze disease is active corrosion, meaning that your bronze item is not protected and is continually corroding. Stress, however, comes in many forms, and some are more effective than others at turning hair white. This same affect occurs when brass, which contains copper, is exposed to bleach. This certainly highlights how easily artifacts of the past can disappear and also how important what remains we do find are! This serves to neutralize the acid that attacks the metal as well as converting the reactive cuprous chloride to largely inert cuprous oxide. H��S�n�0����Y�L�G�D��XT%U7l���1������I�!؂�#;��=�k��S 2�A��`O˹� [2][3], Soaking in sodium carbonate—which does not form a complex ion with copper and is unlikely to affect the patina but is slower than the sesquicarbonate—or benzotriazole (highly carcinogenic) aqueous solutions may also be used. If chloride ions have penetrated beyond the surface more rigorous treatment is required. However, re-exposure of the object to even atmospheric water can restart the process. Then soaking in a benzotriazole (BTA)–ethanol solution to chelate the copper and make it unreactive. To the untrained eye, it may simply resemble a natural patina. �f���ų��9�Q ;�F���/r٬��iQ{)p�C,t����\���ƛ?�v��S�SN���W��s �d�C�r(�{�\�k?���/�������·nH8�x� endstream endobj 18 0 obj 455 endobj 10 0 obj << /CropBox [ 36 36 756 576 ] /Type /Page /Parent 5 0 R /Resources << /Font << /F0 6 0 R /F1 11 0 R /F2 13 0 R /F3 15 0 R >> /ProcSet 2 0 R >> /Contents 17 0 R >> endobj 20 0 obj << /Length 21 0 R /Filter /FlateDecode >> stream Posted at Dec 13/2007 11:21PM: (5) Cu+ + Cl− → CuCl, The reaction then repeats from equation (3). Bronze disease, along with similar visual conditions caused by other moieties, remains an active area of research within object conservation. 3 Cu(OH)2 + 2 HCl, The remaining copper is oxidised by air to the cuprous ion: Pits and holes may be filled with zinc powder, which is then painted over with shellac coloured to look like the specimen. �6K��׍5W|��O��6�QJ���/bƖ�kIkNS�7VH�QN. ��Κ��9����H6퉸��ƞ�����o=q�[Y���B�zy��� H� %PDF-1.2 %���� Amateurs report that the patina may be stripped from the artefact but this is when the solution is boiled so that the carbonate rinse removes the chlorides in hours rather than the cool bath of long duration used by professional conservators. This can lead to serious damage of … Instead of rinses, electrolysis may be used, often with sodium carbonate as the electrolyte and mild or stainless steel as the anode. Rachel Griffith: It seems like theres no end to the obstacles archeologists run into in preserving the past! Harry Anastopulos: Somehow I figured you'd pick this one, Evie. Box 1837 / 60 George Street keffie: Excellent and clearly explained summary of this phenomenon. by Evie. The Journal of the American Institute for Conservation, Volume 29, Number 2, Article 7, 1990. However, while a patina is not destructive, bronze disease most certainly is. It leaves the surface with patches of pale green, powdery material. One of the most effective ways to turn a character's hair completely white would be the stress of prolonged illness.There may be some Truth in Television to this, but typically it's taken to extremes. Bronze disease is a form of corrosion that affects bronze artifacts. The carbonate is similar in effect to the sesquicarbonate. [2][4], "Archaeologies of the Greek Past: Bronze disease", Journal of the American Institute for Conservation, "The Critical RH for the Appearance of “Bronze Disease” in Chloride Contaminated Copper and Copper Alloy Artefacts", "Bronze Disease: A Review of Some Chemical Problems and the Role of Relative Humidity", https://en.wikipedia.org/w/index.php?title=Bronze_disease&oldid=980733656, Conservation and restoration of cultural heritage, Creative Commons Attribution-ShareAlike License, This page was last edited on 28 September 2020, at 04:00.