The numbers 750 stamped on jewelry means that it is 18-karat gold. The jewelry piece is 18 parts pure gold and six parts metal alloy.
One hundred percent gold jewelry is 24 karats. Unfortunately, pure gold isn't very durable, so jewelers add stronger metals to it to keep it from denting. The more alloy in the gold, the more durable it will be, but the lower the karat number, the less value the jewelry may have.
Other common numbers found on fine gold jewelry are 585, or 14-karat gold, and 417, 10-karat gold. The numbers 833 are 20-karat gold, and pure gold will have the numbers 999.
Sterling silver is marked 925. That means that it is 92.5 percent silver and 7.5 percent alloy. Although silver is more durable than gold, the alloy gives it additional strength. Sometimes instead of a number, sterling silver jewelry pieces will be marked with the intials "SS."
Platinum is a popular metal currently for wedding rings. This white metal will usually be marked with a 900 or 950, which is 90 or 95 percent platinum and 10 or 5 percent alloy. Iridium is often the alloy paired with platinum.
Vermeil, or gold-plated jewelry, is usually sterling silver coated with gold. The thick coating can be 14-carat gold, in the case of vermeil, while other gold-dipped jewelry may be plated with 18-carat or even pure gold.