by Scribonius » Sun Dec 01, 2013 9:48 pm
Um... heat usually doesn't, but every now and then Lego gets a shipment of plastic pellets with some kind of impurity in them that causes the plastic to develop cracks over time during normal use - the cracks are usually along seam lines, but sometimes right in the middle of a flat surface. Several of the original Pirate sets that I got when I was a kid developed cracks like those. Doesn't happen often, but it does happen. Could also be from the plastic cooling too quickly during casting so it doesn't "meld" properly...