I was cleaning some of my chips yesterday (keeps me off EBay) and I came up to some of my Chipco chips...and wondered...what causes the "fading" as shown here in the two Fiesta chips I have. The one on the left is not nearly as bright as the one on the right. I assume it's had more use, but is it just that? When I clean other chips I can get a lot of the murkiness off (smoke, dirt, and other stuff I try not to think about), but these...should I try? I've noticed that a lot of my used Chipco chips lack the brightness that the one Fiesta chip has, and I assume that it's just due to age, but...

Is there an answer and/or a solution?

Thanks in advance.