I think maybe I will do that next time. I have a problem with "Forgot-the-laundry-itis" but I will certainly try to do that next time.
This was Arctic White - supposedly a 100% cotton (what it said on the label in large print but in the fine print it said it was 13% poly scrim!) which is why I preshrunk to begin with. The placemat was a chunk of something I had left, it could have been almost anything cotton or cotton poly blend.