Mark,

The Harrah's brass chips got so worn looking because the plastic coating starts to wear off. Some dirt gets into the cracks in that develop in the plastic, adding to the poor appearance of these chips when they worn. Just like any other worn chip, there is nothing you can do to replace what is lost. If you clean it, you can remove some of the dirt, but the plastic will still be worn and cracked. In the end, a worn dirty chip will probably look better than a worn clean chip. That is why there is a large premium on these chips in mint condition.