NOBLE METALS : The strictest definition of a noble metal is metal with a filled electron d-band. According to this definition, gold, silver, and copper are noble metals. Another definition of a noble metal is one which resists oxidation and corrosion. This excludes copper, but adds in other platinum group metals, such as rhodium, palladium, ruthenium, osmium, and iridium. The opposite of a noble metal is a base metal.