Corrosion and oxidation are pretty synonymous terms that you typically associate with metal, not rugs. When metal corrodes / oxidizes, it reacts with oxygen in the air. If the metal is iron, then it will result in rust. When copper corrodes / oxidizes it turns green, like statue of liberty in NYC, and breaks down with time. These are all signs of the passage of time and indications that an item is old.
What people sometimes don’t realize is that when we talk about oxidation or corrosion in rugs, we are still talking metal. Some natural carpet dyes have metals in them and are comprised of materials such as iron, copper, chromium, tin and aluminum to allow the color to adhere to the fiber. Metals and metallic salts make the dyestuff more permanent and lightfast. This means that it will not fade over time, and the colors will, for the most part, stay truer. This is what allows many rugs, carpets and textiles to remain nearly as bright and vibrant as when they were created, even after several hundred years of use.
If the rug is an antique, iron and copper were used, as they were the most common metals used in the color dyeing process. Iron is usually in the form of ferrous sulfate. Copper is usually soaked in vinegar to extract cupric acetate that is then used to dye the cloth. Chemically, these metals act as a bridge between the fiber and the color molecule, allowing it to create a tighter bond.