"But I recall that another layer of ballast was shewn on this diagram. It was below any casks, below the shingle, below the scrap metal, below even the kentledge. It was the thinnest possible layer, a mere membrane, and on the diagram it looked like onion-skin. It was pressed against the tarry inner surface of the hull-planks themselves, and it went by some name such as anti-fouling plates."