This study gathered and reported compositional and descriptive analyses of over 200 Italian Renaissance portrait medals in the collection of the National Gallery of Art, Washington, DC. A statistical model was developed for allocation of these medals into meaningful assemblages, using the surface alloy composition, and an expanded nomenclature was formulated. Copper, zinc, tin, and lead were the primary elements found to combine to form a wide range of alloys. Common impurities were discovered to be significantly lower in the 16th-century medals when compared with those in the 15th-century medals. Renaissance medallists had an extensive knowledge of metallurgy and could produce a variety of alloys without the use of modern technology.