How aluminum foil is made

That shiny side and dull side are an accident of rolling two sheets together at once.

stations: 5
things upstream: 11
raw sources: 6
steps from the ground: 4

The short version

Aluminum foil starts as a thick aluminum sheet that is rolled again and again, cold, until it is a fraction of a millimeter thick. In the final pass two sheets are rolled at once, then peeled apart. The sides that touched are matte, and the sides that met the polished rollers come out shiny.

Cast a thick sheet

Molten aluminum is poured through a continuous caster to make a sheet, in a way that uses less energy than the older route of casting ingots. This is the strip that will be thinned.

Goes in
Aluminum
Roll it down in steps

The sheet is cold-rolled through mills that shrink its thickness with every pass. Foil is an alloy of 92 to 99 percent aluminum.
Double up for the last pass

The rollers cannot get close enough together to produce the thinnest foil, and a single sheet that thin tears. So for gauges below 0.025 millimeters, two sheets are rolled together, doubling the thickness entering the rolls.
Peel the pair apart

After the rolls, the two layers are separated. The sides that pressed against each other are matte, and the outer sides that touched the polished rolls are shiny. The difference does not matter in cooking.
Slit and wind

Circular or razor-like knives trim and slit the foil to width, and it is wound into rolls. Standard household foil is about 0.016 millimeters thick.

End of the lineAluminum foil Next it goes into toothpaste, aspirin, condom and 1 more.

Worth repeating

The first aluminum foil rolling plant opened in 1910 in Emmishofen, Switzerland.
Tobler began wrapping its chocolate in aluminum foil in 1911, including the triangular Toblerone bar.
Foil sparks in a microwave oven, because the fields drive currents through it and voltage builds at sharp points until it arcs through the air.