To clean the bronze Viking brooch, it is recommended to use mild soapy water or alcohol to gently remove dirt and grease. To preserve the patina and the delicate knot pattern in the long term, avoid harsh cleaning agents such as vinegar or citric acid, as well as hard tools like wire brushes, since these can scratch the surface. After cleaning, the piece should be thoroughly dried and ideally sealed with a special care wax or linseed oil to protect the material from further corrosion and maintain its antique shine.