The cut was actually pretty clean.
All the rough look to the edge was the frozen mud. I wet the slate before I cut it an had a wet sponge I tried to keep pressed against the cut-off disc.
The hardest part was keeping everything from freezing. It was less than 10 degrees outside, and me with wet hands. I think we can all tell who the genius was here.
I took the one cut-off inside, and washed it off in the bathtub. A little sandpaper cleaned up the edges very nice.
Here's a photo of the finished cut-off piece. Two of the edges are "factory" and two are cuts that I made. The near edge in this photo is one that I cut. Came out very clean.
http://ecoprojecteer.net/wp-content/...1/DSC_1103.jpg