Tin, Aluminum, Chromium

By Robert L. Wolke
Wednesday, May 24, 2006

Tinfoil has a shiny side and a dull side. Why is this? My co-worker says you should put the shiny side down when covering something in the oven. This doesn't seem plausible to me. What are the facts?

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. Hence, a shiny side and a duller side. When you use the foil, it makes no difference which side is up, down or sideways.

I bought some Reynolds Wrap Release, a nonstick aluminum foil. It works great as an oven pan lining. Even dripping pizza cheese won't stick to it. What is the nonstick coating? Is it Teflon? Can it be used safely at high temperatures?

Reynolds (and its parent company, Alcoa) brought Release to the market in 2002. They will not say what the coating is, except that it is "effective as a nonstick surface and safe for food contact." Reynolds says it is safe at any temperature, including for grilling, and doesn't contain Teflon.

I have heard that cooking in aluminum pots and pans can be dangerous. But what if they're made of hard-anodized aluminum?

Aluminum is the most abundant metal in the Earth's crust. Widely distributed in soil, plants and water, including our food and drinking water, it is impossible to avoid. According to Health Canada, that nation's public health agency, about 95 percent of an adult's daily intake of aluminum comes from food. And less than 1 percent of all ingested aluminum is absorbed by our bodies.

The suspicion of a relationship between aluminum and (take your choice) Alzheimer's, Lou Gehrig's or Parkinson's disease has been floating around for about 20 years. The brains of some Alzheimer's patients have been found to contain abnormally high concentrations of aluminum, but nobody knows whether that is a cause of the disease or a result of it.

Because Alzheimer's is a chronic disease that develops over a long period of time, the long-term ingestion of aluminum in drinking water, which is relatively easy to monitor, should be a logical way to search for a correlation. And yet, epidemiological attempts to link aluminum in drinking water with Alzheimer's disease have been either inconclusive or contradictory.

There is little doubt that whatever aluminum leaks into our foods from cookware is a small fraction of the aluminum we ingest through normal eating, drinking and breathing on our aluminum- pervaded planet.

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