This article deals with the question, to what extent conclusions from the analysis of brass and bronzes can be drawn regarding the authenticity of objects from the Middle Ages. If metal objects were restored, the replaced parts were made of an alloy with a composition similar to the original. Copies from the 19th century, on the other hand, have compositions significantly different from the originals. The brasses used for copies often are characterized by an amount of zinc considerably higher than that of the originals. It is easy to distinguish between original and copy. Such copies, made more than 100 years ago, also were acquired by museums, where they were not always recognized as copies. More difficult is a decision about objects, which, because of stylistic reasons are considered to be copies or forgeries. The difficulty is due to the fact that modern founders also use alloys, which do not differ much from alloys of ihe Middle Ages. A series of analyses of brasses and bronzes from the Middle Ages and from two modern foundries at Berlin shows that not in every case, but sometimes authentic objects and forgeries can be distinguished. In questionable cases, other analytical techniques, like the analysis of the patina or technological examinations, can be applied.