by Dr. Cadmium » Sun Nov 21, 2010 10:44 pm
Both cast zinc (often simply called "diecast") and cast aluminum are silver-gray in color normally but can be coated or painted to look like almost anything. They don't stick to a magnet and they don't spark. They're also both brittle metals and crack apart when struck with a hammer.
To tell them apart:
Cast zinc is much denser than cast aluminum. A comparable piece of zinc will generally way over 2.5 times as much as a piece of aluminum.
Cast zinc usually has a slightly bluish-tone that becomes easier to recognize with experience.
Cast zinc pieces are often more detailed than cast aluminum, though not always. Things like gears, door hardware and ornate fittings.
When in doubt, use the nitric acid test, assuming you have basic knowledge of chemistry and safety. Concentrated nitric acid reacts instantly and aggresively with zinc, producing brown smoke (note if you get white precipitate in addition to brown smoke you have tin, Sn). Reactions with aluminum are minimal.