Terry,

Although you did not specifically rule out this rationale, I think that the chips pressed up against your chips were identical chips, i.e., boxes of the brown with 3 blue inserts chips.

The heating of the chips, which as I understand it was a fire very near to stacked boxes of the chips, was enough to slightly fuze (very sligtly!) the insert material of one chip surface to the other. This action, in effect, mixes the color brown (which is heavy with yellow pigment) and blue (the inserts) to yield a thin green coloration! (Yellow and blue mix to be green. Try it at this website: http://painting.about.com/library/blpaint/blcolormixingpalette1.htm click yellow and then click blue!)

I would contend that the two chips on either side of yours have the same greenish staining. Only the chips at the ends of the stacks are stain-free on one side.

Thanks for the images.

Jim