Simple marks are easy to make, and fun.
These were made by tools that were gifts from friends.
A simple chattering tool is held angled in the hand in different ways to make larger or smaller marks. This is simply a strap of flexible, bent metal with sharpish edges. Held a little out from the pot, it makes thinner lines. Held about perpendicular to the pot, it makes bigger, wider marks. Little chippy shavings come off as the tool bounces on the turning pot, and it makes a sort of whirring hum.
The little doodad below is a lemon zester. It gets pulled along the surface as you turn the bowl in your hands bit by bit.
Below is one of my usual trimming tools, used to trim excess clay from the bowl after it has firmed up quite a bit post-throwing. It made uncomplicated rings around the bowl.
(This is a Bison trimming tool, handmade in Las Vegas. Expensive, but worth it. It stays sharp.)
Here (below) is a link to a video of much more complicated surfaces made by Ken Standhardt on his beautiful pots, with tools just as simple as the ones above- a pair of can opener/punches, in fact, and a ballpoint pen. So much is possible using the most elementary tools! http://www.opb.org/television/programs/artbeat/segment/sculptor-kenneth-standhardt/
Human ingenuity used for good, not evil. Ohhhh yeah.