I have usually been working with blank CD’s for using my blender pens, etc..  Last night though, I decided to do some watercolor.  So…the CD wouldn’t cut it because of the hole in the middle.  So I decided to use one of my acrylic blocks.  It was great!!!!  I could add water to it and have nice control over the brush and you just have to rinse it off really fast and then you have an extra clean block!  Give it a try!