Duke,

What I believe you have is a dirty one. I've seen them in various stages of this and whatever it is is hard to remove. I've seen the same thing on other yellow chips of this type.

I don't know what causes it. Perhaps the chemical compostion of the chip. Maybe something in the air or something common on the hands of people in the area.

For example, many of the $1 bills here in Wellington have a yellow tint to them due to a chemical used in one of the factories here. It gets on the workers hands and is soon transferred to the currency.

Greg