@Sierra02 - I've tried that technique before with the bread slices. It was worthless to me. All I could manage to scrape off was about a teaspoon of sugar.
A clay disk is the only thing I use to soften my brown sugar with nowadays. I've even made my own before out of an old clay pot. Just break it into pieces, smooth off the edges, wash it and place it in your sugar. It works just as well as the fancy store bought ones.