Which of the following is NOT a method for identifying metal?

Magnetic resonance is not a conventional method for identifying metals in practical plumbing applications. Instead, it is a technique more commonly associated with medical imaging (like MRI) or scientific research rather than a straightforward assessment of materials in a field setting.

In contrast, visual appearance and color can provide initial clues about a metal's type; for instance, copper is reddish, while aluminum is typically silver. Examining a fractured surface can reveal characteristics indicative of specific metals, such as grain structure or brittleness. Relative weight is also useful since different metals have distinct densities, allowing for identification based on how heavy or light a material feels compared to others. Therefore, the most appropriate methods for identifying metals in practical scenarios would not include magnetic resonance, which is why that choice is correct.