The Mohs hardness of lead is about 1.5, while the hardness of silver is above 2.5, and the lowest hardness of iron is 4.
If the metal block were cast in lead, the scratches would be deeper. This level of scratching suggests it is indeed silver.
As for the reason for placing silver blocks in the water bucket, Chen Zhou thought it might be for purifying drinking water.
Although he did not know when the antibacterial use of silver originated, there are many museums in his hometown with Yuan dynasty relics. Through school-organized museum day trips during middle and high school, Chen Zhou learned that as early as the Yuan dynasty, the Mongolian Nobility used silver flasks to preserve mare's milk to prevent spoilage.
Presumably, a few hundred years later in Europe, using silver for purifying drinking water wasn't really an obscure knowledge.
