Why does aluminum foil have one shiny side and one with a matte finish?

Ever think about that?

And wonder which side should face the food?

Robert L. Wolke, in his "Food 101" Washington Post column, explained it all for us.

Here's what he wrote:

First, a brief bit of history.

In the 19th century, Thomas Edison invented a phonograph machine, in which a sound-driven vibrating needle impressed grooves into a cylinder covered with a thin foil of the soft metal, tin.

In the 20th century, tinfoil was being widely used as a wrapping material for foods and drugs.

By the middle of the century, tinfoil had been replaced almost completely by thin foils of a different metal called aluminum.

Yet many people persist in calling aluminum foil "tinfoil."

We chemists get annoyed at things like that.

Get with it, folks!

This is the 21st century!

Now, about aluminum foil.

Aluminum foil is made by rolling sheets of 98.5 percent pure aluminum metal between pairs of polished, lubricated steel rollers.

Successive passes through the rollers squeeze the foil thinner.

Household aluminum foil is so thin (0.0005 of an inch) that the rollers can't handle it without tearing it.

The final rolling is therefore done on a sandwich of two sheets, face to face.

The outer surfaces emerge with a finish as smooth as the rollers, while the two face-to-face inner surfaces emerge with a matte finish.

The two sheets are then separated.

Hence, a shiny side and a duller side.

When you use the foil, it makes no difference which side is up, down or sideways.

-----------------------

FunFact (from the same column, different question): "Aluminum is the most abundant metal in the Earth's crust."

In 2005 a group of researchers from MIT published the results of perhaps the most rigorous study ever performed to investigate whether aluminum foil helmets serve as a protective measure against invasive radio signals.

Below, one of the investigators.