Soda Can Experiment Update - July 7, 2010

So you may recall that I've found lots of corroded and rotted aluminum cans at the beach. And that I started an experiment to see if I could recreate the conditions that cause a can to rot. My last update was more than 3 weeks ago, so I wanted to drop another quick post.

A really quick post. What's changed in 3 weeks?

Not a lot.

New corrosion may be happening, but it's going so slowly that there's nothing really to show.

My hunch is that the exposed metal has oxidized, leaving very little surface area of fresh aluminum to react with the salt and corrode.

Thus, another rethink (or perhaps "threethink" at this point). I was so busy narrowing things down that I think I lost sight of the forest. The beach isn't one event, it's a system. It's sand, wind, salty air, wet times when the tide comes in, starkly dry times when it goes out. People kicking things around, burying them. It's dynamic, unpredictable. It's not a can sitting in a bucket of water on a countertop for a month.

So, my rethink: Make a soda can experience real beach conditions. A can should be drunk, crushed, shaken around in wet sand, shaken around in dry sand, tumbled, rolled, exposed to bright light, buried. Only by doing that will I be able to say whether it was a beach environment that causes a can to rot like those that I've collected.

More to follow!

Experimental archaeology

Instead of just thinking about how people used to make tools, build walls, create things, archaeologists are now actually doing it themselves. By experimenting, hands-on, they've overturned many venerated theories, and opened up new ones. It's an exciting field that has cast new light on everything from how Bronze Age Britons built Stonehenge to why Civil War weaponry & tactics were so deadly.

It's also useful for understanding how & why artefacts decay -- how they meet their end. I'm excited now to be tossing my hat in the ring.

I had asked a question about aluminum cans rotting at the beach.

I wanted to learn just what makes a soda can break down like the ones I had collected, and how long it really takes. It turns out, there are actually some really interesting experiments with how to corrode aluminum cans. But nothing that I found showed the natural effects of beach and ocean and salt.

So I decided to do an experiment of my own. From what I had learned, it seemed a can doesn't rot just because of seawater -- it also needs iron nearby to help it corrode. This seemed a good place to start my test. I would run a controlled experiment -- I'd put two cans in two buckets of seawater. One bucket would have iron nails in it, the other wouldn't.

This morning I grabbed an empty 5-gallon bucket from our condo's basement, went to Ocean Park, and filled it up in the ocean. I stopped at Hannaford's and picked up a 12-pack of ginger ale, then headed home. Cut the tops off of two milk jugs, emptied two of the cans (but left them unwashed to better simulate a can tossed out at the beach), and grabbed a handful of nails from the toolbox.

At 9:15AM, 5/25/2010, I filled each milk jug up with 2 1/2 quarts of the seawater, dumped the nails into one of the jugs, and put one can in each jug.

Lastly, I put a little clingwrap lightly over each jug to slow evaporation but still allow oxygen from the air to get in, and set the jugs off in a corner.

The next step is simple -- just wait and see what happens. Maybe nothing, maybe an answer. Stay tuned!