The staircases to the right and left sides of the wooden gate each have a pair of cornerstones. I began by making a wood frame to sculpt my cornerstone on.
The wooden frame was notched out to fit over the staircase steps. This way as the sculpting progressed I could test fit my cornerstone exactly where it would later be mounted.
Using Super Sculpey I modeled my cornerstone. I textured it and added a few cracks then smoothed down any rough areas with a stiff brush dipped in 91% alcohol. Since I would be needing multiple cornerstones I decided to make a latex mold of my original model and cast the four pieces.