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Message:: [QUOTE="2manybooks, post: 9562284, member: 8267"]Welcome ,[USER=83001]@Natalia006[/USER]. "Patina" is an imprecise and somewhat subjective term. As one of my professors noted, "one man's patina is another man's dirt". It usually refers to signs of use and age that are considered desirable. With regard to metals, the term "patination" also refers to deliberate treatments that were applied to create different surface colors when an object was made. It is important to consider the possible presence of such altered surfaces when making decisions about cleaning metal objects. Not everything was meant to be uniformly shiny, and it is unfortunate when over aggressive polishers remove original features of an historical object. In the case of the green deposit on your turtle, it would be considered an undesirable corrosion product, as verybrad noted. Green corrosion products on copper/copper alloys can be of several different compositions, depending on the type of contaminant that has reacted with the copper. Acidic contaminants can cause various forms of copper acetate, commonly called verdigris. Some forms are soluble in water and ethanol, other forms are more soluble in acids and ammonia. Long exposure to (clean) air creates basic copper carbonate, a form of copper corrosion that is quite stable and actually protective of the underlying metal. This is the type of corrosion that used to form on copper roofs and bronze statuary exposed outdoors. Unfortunately, modern air pollutants now tend to convert the copper carbonate to a copper acetate which is more soluble in rain, resulting in the gradual dissolution of the metal. Salt contamination (from such exposures as sea water, some soil types, and frequent handling with sweaty fingers) can cause copper chlorides to form, which are a particularly pernicious form of corrosion. This is the type referred to as "bronze disease". Contact with fatty acids such as those found in leather, leather dressings, and human skin can cause the formation of waxy green deposits of copper stearates. In the case of your turtle, it looks like the green area is associated with remnants of the clay material used to make the mold, which may have left either acidic or chloride containing contaminants. You might try cleaning it with vinegar (a mild acid), as bercrystal suggested, being careful to wash the vinegar off using distilled water, and dry it thoroughly. You might even want to put it in the oven on a low setting to make sure all of the moisture is driven off. Check it over the next few days and weeks to see if any bright blue-green spots reappear, which could indicate the presence of chlorides.[/QUOTE]

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