And this is what came out! I was upstairs when Scott removed them from the washer, and I could hear him exclaim when he saw it! He was shocked, to say the least! What could I say? We had a good laugh over it, and now I have to decide how to proceed.
Last night, I hand washed all of my completed blocks and letters, and I think I can salvage all but about 4 of the letters. I could definitely tell which ones had the "bad" black fabric - it left a ring in the sink! Apparently, the acids in cardboard boxes leach into the fabric, and cause it to break down. I had just never seen proof of it until now!