Mad about Science: Aluminum foil

By Brenden Bobby
Reader Columnist

It’s easy to take some of our most ubiquitous kitchen items for granted. They’re relatively inexpensive, always within arm’s reach and quick to replace with a quick trip to the grocery store.

Now try to imagine if you had to produce some of your favorite kitchen items at home. A crafty individual with a handful of bricks, some tongs and a sharpening stone could likely make knives and cutlery. But what would you wrap your food in?

Throughout much of human history, preservation of food was accomplished with salt and linen. Linen in particular was often coated in beeswax to create a better seal to keep air and moisture out of foodstuffs. When the beeswax became gross and the linen needed to be cleaned, individuals could simply melt the beeswax, wash the linen and reapply the wax as desired.

This was apparently tremendously inconvenient, because we started wrapping our food in metal with the invention of tin foil.

Tin foil and aluminum foil are not the same thing. We informally refer to metallic foils in America as “tinfoil”, but tin foil and aluminum foil are two different inventions filling the same role. That roll of metallic foil in your kitchen isn’t tin, it’s aluminum, and it has been for as long as virtually anyone reading this article has been alive.

Proper tin foil is a far older invention. We have evidence of tin foil being used as decoration as far back as the fifth century C.E. in China, and I know what you’re thinking — no, it wasn’t for a hat.

While tin and aluminum can both be used to construct a Faraday cage to block radio signals, doing so requires a great deal of precision. Gaps in the material render it virtually useless for that purpose, and if you’re trying to wear it to protect your brain, realize that the entire lower two-thirds of your skull will remain exposed. Sorry, folks, radio waves can still pass through flesh and bone. If it couldn’t, Wi-Fi wouldn’t be very useful. 

Luckily, despite what your aunt might tell you on Facebook, radio waves don’t possess the energy required to damage DNA unless you’re standing really close to a very powerful source point, which can cause burns. The government also can’t read your thoughts with radio waves — it just pulls the browsing data from your cellphone carrier to do that.

Tin foil in the kitchen first started appearing in the early 20th century. Being metal, tin foil was oven-safe and made cleaning up pans a breeze. Its malleable nature also allowed for it to cover and seal food to keep out pests and bacteria. This role was also well suited to plastic wrap, which was invented in 1933, moving in lockstep with household refrigeration, which became more widely available in 1927.

Aluminum foil as we know it replaced tin foil by 1910, with the operation of the first aluminum rolling plant in Emmishofen, Switzerland. We’ve explored the process of refining aluminum in previous installments of “Mad About Science,” but here’s a brief overview of the process in order to put the opening statements of this article into perspective:

Bauxite ore is broken down in high-temperature caustic soda in something called the Bayer process. Aluminum doesn’t exist as a shiny metal in the natural world — it must be converted from bauxite into aluminum oxide using this process. Next, the aluminum oxide is dissolved in molten, electrified cryolite, allowing the pure aluminum to settle at the bottom and be tapped off to create ingots or rolls in what’s called the Hall-Héroult process. This is primarily why creating your own aluminum foil at home is virtually impossible.

This is an extreme simplification of the process, and if you’d like to see a more in-depth exploration of the process of how aluminum and aluminum foil is made, the Factora channel on YouTube has a fantastic visual breakdown of the entire process.

Finished aluminum ingots are run through multiple stages of hot and cold rolling to smash it into a desired thickness. This involves running a heated ingot through different stages of steel rollers that press down the malleable metal little by little, until it’s cooled to room temperature and smashed further.

Standard household aluminum foil has a thickness of 0.016 millimeters, while foil marketed as “heavy duty” is 0.024-mm thick. While this doesn’t sound like much, it’s a pretty noticeable difference once you use it in the kitchen. Foil wrappers for things like fast food burgers are much weaker and prone to tearing than foil used on dishes of Thanksgiving leftovers.

Aluminum foil is also commonly used to clean silver and gold jewelry. It is highly conductive and has a high surface area, which makes it great to use for electrolytic cleaning —  a process of submerging aluminum foil and jewelry in water and a baking soda solution, then passing an electric current through it. A chemical reaction with the sodium bicarbonate loosens contaminants and corrosion from the jewelry, while gas released from the process creates a scrubbing action.

Aluminum foil is generally recyclable. Recycling aluminum products uses 5% of the energy it requires to create new aluminum products from bauxite. This level of intensity is rarely seen in any other manufacturing process, especially when you consider that aluminum, unlike paper, can be effectively reused as many times as it’s recycled.

Stay curious, 7B.