
As you can see in the photo, the felting stone fits in the palm of your hand. Unfortunately, that lovely hand in the photo is not my own. It actually belongs to looseends (a.k.a. Melissa) on flickr. I thought that it was such a nice photo that I certainly could not do better taking one of my own so I borrowed it for my post and according to flickr's Creative Commons license. A big thank you to Melissa for her lovely photo of this useful little tool.
It is small, but certainly handy and time saving. As you can see from the photo, it has rows of ridges that increase the friction when rubbed against your wool during wet felting. I do suggest that you wait to use it when the wool has a top layer of skin formed or is at a the medium or mid-felted range so that it does not tangle in the loose wool fibers. It makes quick work of the latter stages of wet felting and also saves your hands from getting roughed up.
I purchased mine from Mielke's Fiber Arts, but you can also get it from Halcyon Yarn where Melissa purchased hers. At the time I purchased the felting stone, I also purchased a plastic felting mat which has proven to be quite useful and time saving too. I recommend it as well, and it is very inexpensive so it won't break the bank, but it hopefully will improve your felting.
Happy felting! I hope to have some photos of my newly felted items to show you soon. Right now, I'm a feltmaking fanatic though so as soon as I slow down a bit, I'll take some photos to post.