Jewellery pieces are made from precious metals such as gold, silver and platinum in the form of an alloy (combined with other metals) to ensure the technical characteristics required to make a piece, such as hardness and colour.

The amount of gold present in the alloy of a piece of jewellery (technically referred to as the "gold fineness") is indicated through the hallmark, which is simply a symbol applied by the Imprensa Nacional Casa da Moeda.

The term "ouro de lei" (legal-standard gold) refers to any type of gold permitted by law. In Portugal, this term refers to a gold alloy of 19.2 karats, because out of 24 parts of the metal alloy, 19.2 are gold, meaning the alloy contains 80% gold (which may also be referred to commercially as 800 gold, or Portuguese gold).