Hi Gerald,
First I do not take any responsibility for the suggestion I am giving you. If you carry it out it will be at your own risk. That being said, you can try using a very soft pencil eraser. The type of eraser that is sold in most office supply stores. Rub it very carefully center out until the oxidation is removed. It may slightly change the color of the chip (lighten it) but if done correctly it will not hurt the chip in the sense of making it undesirable.
Jim