The bronze alloy in the sculpture contains inadequate tin, leading to flaws.

Evidence

There clearly wasn’t quite enough tin in the alloy, which explains why the surface is rather pock-marked, and also why the structure is weak, so that the hind legs of the bull have broken off. — Neil MacGregor, A History of the World in 100 Objects, 322

Categorization

• XREF: The imperfections in the sculpture provide insight into ancient metalworking practices and resources.
• corroborated: 2 independent passages support this claim — Neil MacGregor, A History of the World in 100 Objects, 322