Q: Why do metal zipper teeth corrode after washing?
Corrosion after washing usually comes from three sources: chlorine or bleach in the wash, aggressive detergent residue left in the chain, and moisture trapped against the tape during drying. Chlorine attacks the plating and the base metal quickly, producing pitting and a green or white deposit. Even a small amount in a shared laundry can affect a whole batch.
Dissimilar metals accelerate the process. If the slider is a different alloy from the teeth, or if the garment has metal buttons and rivets, a small galvanic cell forms in the presence of moisture and salt. Plating porosity is the other factor: a thin decorative finish may look correct but expose the substrate at the edges and inside the slider channel.
Prevention is a specification issue. Choose a corrosion-resistant finish, confirm salt-spray performance, and state that the garment must not be chlorine-bleached. For after-sales diagnosis, distinguish surface staining that can be cleaned from pitting that has removed the plating; the first is a care issue, the second may indicate an inadequate finish for the intended use.