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Name: Terrance
Status: student
Grade: 9-12
Location: TX

Why is aluminum foil shiny on one side?

Hi Terrance,

The reason aluminum foil is shiny on one side and dull on the other is rather interesting. Aluminum foil is produced by rolling it between successive steel rollers. Each set of rollers squeezes the foil thinner. The last stage of rolling reduces the foil's thickness to a thousandth of an inch or even thinner. The problem is that such a thin foil is too easy to tear during the last rolling stage. So, for the last stage of rolling, two sheets of foil are placed face to face and passed though the final set of rollers together. Since the steel rollers are highly polished, the foil faces that contact the rollers are also embossed to a highly shiny surface.

After rolling, the resulting sheets are separated from each other. The surfaces of each foil that had faced each other are matte in texture, since they had only been squeezes against each other, and not the polished rollers.

Bob Wilson.

The fact that one side of aluminum foil is shiny is an artifact of the production process.

Aluminum foil is produced by passing ingots (bars) of aluminum through metal rollers. Successive passes through the rollers with the rollers being brought closer to each other makes thinner and thinner sheets.

However, to make the aluminum foil used in the kitchen, the foil gets so thin, the rollers so close to each other, that passing it through the rollers can cause tearing (the foil can sometimes stick to the rollers or it may crimp up or buckle and so on). To avoid this, two layers of foil are passed through the rollers. The double thickness prevents all the issues that cause tearing to happen while still getting to press the foil into a desired thickness for each sheet.

Since the rollers are very smooth and hard, the side of the foil that is facing the rollers gets smooth and shiny. The side that is facing another foil (the middle area) gets a matte finish.

There is actually little difference to the matte and shiny finish. Without instruments, the difference heat reflection or heat containment of the shiny side would not be observed.

Greg (Roberto Gregorius)

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