Why does aluminum foil turn black?

The aluminum foil in your home sometimes turns white, or even gray or black. What causes this, and can you still use it? Today we'll explain.

Natural Oxidation and Protective Oxide Film:

Aluminum in air quickly forms a dense aluminum oxide film (Al₂O₃) approximately 1-5 nm thick. This film prevents further oxidation of the aluminum foil. This oxidation is normal and generally does not affect the functionality of the aluminum foil.

Exposure to water before the protective film is formed:

Before use, aluminum foil rolls are in a rolled-up state, with insufficient exposure to air and an incomplete oxide film. If exposed to water, rain, or humidity, the moisture reacts chemically with the aluminum, forming loose oxidation products (such as Al₂O₃·3H₂O), causing the surface to turn black or dark, or even show signs of corrosion.
 

How to Prevent Aluminum Foil from Turning Black
1. Seale the foil in a sealed container and place in a desiccant container to avoid contact with moisture.
2. Store in a dry, well-ventilated area, away from high temperatures and humidity (such as in the bathroom or near the kitchen sink).

3. Do not store in a damp refrigerator or wet warehouse.

4. Avoid temperature differences: When moving from a cold environment to a warm place, wait until the temperature matches the ambient temperature before opening to prevent condensation.

Treatment of oxidized aluminum foil:

If the surface is only slightly oxidized (darkening), you can gently wipe it with a soft cloth dipped in neutral detergent; if it is severely corroded (blackened), it is recommended to discard it because the oxide layer may peel off and contaminate food.

Shanghai Mengjiang Aluminum Co.,Ltd has specialized in producing aluminum foil for over 17 years and export 4000 tons per month. Welcome to contact us via email: inquiry@cnaluminiumfoil.com or whatsapp:008613661547963.