With silver cleaner from Markus Brüche, it works very well. The slightly purple patina in the photo is black/grey though; I didn't get the ideal light.
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Markus Wehmer 6.3.2024
Keep your hands off citric acid!!! And the general rule is: do not use chemicals before the finds have been submitted to your local monument authority/archaeological department. From a restorer's point of view, most of the "treatment methods" that are circulating are at least questionable and often even catastrophically bad for the finds!