A, to copper alloy (copper-nickel alloy, copper, brass) made of metal zipper causes:

When used in metal products or wool products, the metal zipper will be part of the metal oxidation caused by the phenomenon of black teeth. This is because the leather manufacturing leather and wool products on the processing bleach, etc., in the process and remain in the product, the gas products will cause the metal zipper discoloration.

Examples of chemical reactions: oxidizing bleach (H2O2) → black (CuO) or red (CuO2);

B, rubber bands bundled metal zipper causes:

Rubber band itself contains sulfide, rubber band bundled metal zipper, the metal sprocket will produce vulcanization (black).

Chemical reaction example: sulfide or HS2 gas excess conditions → black [CuS]

C. Causes of discoloration due to contact with an acidic compound or a chromium compound.

Examples of chemical reactions are: acidic compounds and chromium compounds [Cr2O3] → black [CuO, red [CuO2] or blue [CuSO4].