Genuine gold leaf is pure gold (or nearly pure—23.75 karat is standard). It is chemically inert. It does not oxidize, does not tarnish, does not change color over centuries. Imitation leaf is typically brass—an alloy of copper and zinc. It looks like gold initially, but it is chemically active. Copper oxidizes. The surface darkens, turns green, loses the bright reflectivity that makes it appear golden.
The difference goes deeper than tarnishing. Real gold leaf has a specific weight, a specific malleability, a specific way it responds to pressure and burnishing. It accepts engraving and scratching with a particular character. Imitation leaf is lighter, more brittle in certain ways, less forgiving of heavy-handed burnishing. The way light reads on genuine gold is subtly different—warmer, more complex—because of how pure gold absorbs and reflects light compared to brass.
For long-term work, genuine gold is the only choice. For NoirGold.Art, the commitment to material authenticity means genuine leaf. The work is meant to last. That requires real gold, not an imitation that will age into something else.