The most helpful tool for testing metals is a magnet. If it sticks to a magnet, the base metal is steel or nickel. Pot metal has a weak attraction to a magnet also. If it does not stick to a magnet, it could be a variety of metals: aluminum, brass, silver, gold.
Aluminum is relatively light in weight. It is normally silvery in color but can be anodized with a durable gold finish. It was used quite extensively by the West Germans in the late 50's and 60's. I have discovered, however, that it was used in the early 20th century and was used for some metal beads in Czech jewelry from the 1930's.
Alpaca is a metal alloy that does not contain any silver, but looks somewhat like it. Alpaca does not turn light or shine brightly when cleaned with a silver polish.
Brass is relatively heavy, yellowish in color, and when rubbed several times with the fingers, will leave black on the fingers from the tarnish of the brass.
Metallized plastic is relatively light in weight also and can be recognized by a "fat" edge to the bead hole. Sometimes one can see the blue acrylic lining. The most common acrylic linings I have seen are blue/green or white.
Pot Metal is heavy, silver colored, and soft. It can often be bent with finger pressure and will mark if medium pressure is applied with a pliers. It can be heavily plated with a "painted" look, but can also have a thin coating of gold or silver over the metal. Because it is a soft metal, jewelry designers must make pieces using pot metal thicker than brass or harder metals so that it holds up to ordinary wear.
Silver made in the last 80 years is usually marked sterling or 925. The 925 mark is rarely seen on jewelry made in the USA until 1976 when the laws regarding fine metal content were strengthened. Silver marked "silver" may have some silver content, but it is less than 925. Items marked 800 are not sterling, but do have 800 of 1000 parts silver. Much of the jewelry made by Native American artists of the past was not marked for silver content but often tests as sterling.
Gold and Gold Related: The mark 14kgp means gold plated. Similarly, 14kge means gold electroplated. Though jewelry made before 1910 may not be marked, most gold jewelry made during this century is marked with either the carats or a number stating the parts of gold per thousand. The number 585 means 14k gold. Anything marked 1/20 before 12k or 14k means that the item is gold filled. Gold-filled jewelry could also be marked 12kgf.
Vermeil is gold plated metal. It usually has come to mean gold plating over sterling silver, but Webster's Dictionary says that vermeil can be gold plating over a number of base metals. A marking of 925 on an item that looks gold would designate vermeil with a base of sterling silver.