The Copper Counterfeit

Your uncle is furious. Last week a smooth-talking man at the Sunday market sold him a "solid copper" lucky coin — heavy, warm-coloured, shining like a small sun — for eight hundred rupees. "Real copper," the man swore. "It will bring money to your house." Your uncle believed him. Then yesterday your uncle dropped it, the corner chipped, and underneath the copper shine there is a dull grey. Steel. The coin is a cheap steel slug with a copper skin thinner than a coat of paint. He has been robbed — and worse, he does not understand how. "You can't just paint copper on steel," he keeps saying. "It rubs off. This didn't rub off. How did they do it?" You are going to show him exactly how — by doing it yourself, in twenty minutes, at your own table. Here is the trick the market man knew and your uncle didn't. Copper doesn't only come as a solid lump. Drop the right blue crystals into water and the water fills with copper, spread out so fine you cannot see it — but it is in there, floating, waiting. Now give that water a gentle electric push from a battery, and the copper stops floating and starts travelling: it creeps out of the water and packs itself, atom by atom, onto any piece of metal you connect to the right wire. In a couple of minutes a plain grey steel object comes out wearing a skin of real, shining copper. Not paint. Real copper — that is why it doesn't rub off. That is how you fake "solid copper" for the price of a battery. So the counterfeit isn't magic and it isn't paint. It is a cell: two pieces of metal standing in blue water, a battery pushing copper from one to the other. Build that cell, run it once, and you will have made your own "solid copper" coin from a steel slug — and you will be able to hand it to your uncle and say, this is what he did, and this is how I know. Today, your team is going to build one.