The small amount of Columbium (later named Niobium) was supposed to make the metal hard to reproduce and the tokens hard to counterfeit. It also allowed Franklin Mint to patent their alloy .

By the way, the white cards that Franklin mint used as token holders were not meant to last for 50 years, and lots of the tokens that were kept in these developed corrosion on the edges. This is more common when the cellophane encasing the holder developed little cracks and allowed moisture in.

Although I still have a lot of them in original cards, it's best to take them out and put them in a plastic holder that's less likely to corrode the edges. I haven't found any way to salvage a token with this kind of damage to it.