Yes it was a challenge, since there's lots o' little dimples in those stones! I used a Sharpie extra fine point permanent marker only, for this little rendition on a grey stone, of CZT Carol Ohl's pattern named Puf. Be sure to visit Open Seed Arts to see Carol's tutorial.
The next pebble is a dappled oatmeal colour. Visit Linda Farmer's Tangle Patterns site to read information on the origins, and drawing of Hollibaugh pattern.
After drawing in the pattern there was no way I could've filled in with black, but then remembered I have a Pigma brush marker. This made for a more intense line as I overdrew the original lines, and the filling in, became more a painting process with the flexible brush tip.