By Pat Loeb

PHILADELPHIA (CBS) – The U.S. Mint in Philadelphia is conducting tests on new materials for coin-making. Copper and nickel have gotten too expensive.

A penny costs more than two cents to make; a nickel, more than 11. Mint spokesman Tom Jurkowsky says, that just is not sustainable.

“We’re undertaking a very aggressive effort to see if we can’t find more cost-effective alternative metallic coinage materials– different elements, different metals, different alloys.”

Jurkowsky says it’s not easy. The mint has to find a way to make them cheaper, but still substantial.

“You look at some of the coins in your pocket and it’s not unusual to, say, have a quarter, a dime, nickel, whatever from the 70′s. It’s one of the things about coins. They last a long time. But that’s with the current materials. Will a coin (made from other material) — will it last 30 or 40 years? That’s the kind of thing we have to ask.”

They also have to have the properties that make them recognizable to meters and machines.

“If you can’t put an electromagnetic field in it that will work in a vending machine, it’s not going to work.”

Jurkwosky says, though silver is more precious than nickel or copper, dimes and quarters still cost less to make than they’re worth, though he says the mint is looking for ways to make them even more cheaply.