What .925 Sterling Silver Means

The number is a ratio, not a brand or a grade. It tells you what the metal is made of.

The number

.925 means the alloy is 92.5% silver by weight. The remaining 7.5% is other metal, usually copper.

The US National Stamping Act allows a piece to be called sterling silver only at that ratio or higher. Below it, the term can't be used.

Why not pure silver

Pure silver — .999 — is too soft to hold a shape. A ring made of it bends against a door handle; a setting made of it releases the stone. The 7.5% of copper is what gives the alloy enough hardness to survive being worn.

The trade-off is tarnish. Copper reacts with sulfur compounds in air and on skin, and that reaction is what darkens silver over time. Pure silver tarnishes far less, which is exactly why it isn't used.

Solid, hollow, and plated

Three constructions look similar in a photograph and behave differently in the hand.

• Solid cast — metal throughout. The piece weighs what its size suggests, and relief cut into it stays put under handling.

• Hollow — a formed shell with air inside. Much lighter for the same size, and prone to denting or bending under pressure. Not a defect, but a different object.

• Plated over base metal — a silver-colored layer over brass or another base metal. What's underneath is what remains when the surface wears.

A listing that gives a weight in grams lets you check which one you're looking at. A listing that doesn't isn't necessarily hiding anything, but it's the number to ask for.

What the marks mean

On a piece of sterling silver you should find:

• .925 or 925 — the fineness mark, stating the ratio

• A maker's mark — the registered name or symbol of whoever is responsible for the piece

US law requires the second whenever the first is present. A fineness mark with no maker's mark beside it is a gap worth noticing.

Oxidized silver is not tarnish

Some pieces are deliberately darkened in the recesses to make relief read against the polished areas. This is a surface treatment applied on purpose, not neglect and not damage.

It wears differently from the metal underneath, and chemical dips meant to remove tarnish will strip it in seconds. If a piece has an oxidized finish, its care instructions are different from plain polished silver — check them before cleaning.