During my casino trip this summer, I always put the chips I had bought in the glove compartment of the car. After one week, one white chip turned red from the $5 chip below. I thought that the heat in the car was the cause.

After returning home I stacked all the chips from my trip on the bookshelf. After two weeks the $5 chip at the bottom of the stack left a red impression on the book shelf and I can't remove it!

What's the cause of this? Is this a problem of only certain chip manufacturers?

Any help is appreciated! If you have read my previous posts, you know I have little knowledge about chips because I collect dice and the only chips I have are for trade...